chore: regenerate README (#205)

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<details><summary>Log from Synthtool</summary>

```
2021-06-30 16:38:10,805 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-security-private-ca/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-06-30 16:38:12,164 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

```
</details>

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.github/readme/synth.metadata/synth.metadata

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-security-private-ca.git",
-        "sha": "f6b2f1e237a08aa7563af3fb0929960bb03092c0"
+        "sha": "161d88df6b8461154b756ee3bb70f253802f52ef"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "c72e5beaba53532dc561094b2d8483e4da06921d"
+        "sha": "39652e3948f455fd0b77535a0145eeec561a3706"
       }
     }
   ]

README.md

@@ -62,6 +62,26 @@ use this Certificate Authority Service Client Library.
 
 
 
+## Samples
+
+Samples are in the [`samples/`](https://github.com/googleapis/java-security-private-ca/tree/master/samples) directory. The samples' `README.md`
+has instructions for running the samples.
+
+| Sample                      | Source Code                       | Try it |
+| --------------------------- | --------------------------------- | ------ |
+| Create Ca Pool | [source code](https://github.com/googleapis/java-security-private-ca/blob/master/samples/snippets/cloud-client/src/main/java/privateca/CreateCaPool.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-security-private-ca&page=editor&open_in_editor=samples/snippets/cloud-client/src/main/java/privateca/CreateCaPool.java) |
+| Create Certificate | [source code](https://github.com/googleapis/java-security-private-ca/blob/master/samples/snippets/cloud-client/src/main/java/privateca/CreateCertificate.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-security-private-ca&page=editor&open_in_editor=samples/snippets/cloud-client/src/main/java/privateca/CreateCertificate.java) |
+| Create Certificate Authority | [source code](https://github.com/googleapis/java-security-private-ca/blob/master/samples/snippets/cloud-client/src/main/java/privateca/CreateCertificateAuthority.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-security-private-ca&page=editor&open_in_editor=samples/snippets/cloud-client/src/main/java/privateca/CreateCertificateAuthority.java) |
+| Delete Ca Pool | [source code](https://github.com/googleapis/java-security-private-ca/blob/master/samples/snippets/cloud-client/src/main/java/privateca/DeleteCaPool.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-security-private-ca&page=editor&open_in_editor=samples/snippets/cloud-client/src/main/java/privateca/DeleteCaPool.java) |
+| Delete Certificate Authority | [source code](https://github.com/googleapis/java-security-private-ca/blob/master/samples/snippets/cloud-client/src/main/java/privateca/DeleteCertificateAuthority.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-security-private-ca&page=editor&open_in_editor=samples/snippets/cloud-client/src/main/java/privateca/DeleteCertificateAuthority.java) |
+| Disable Certificate Authority | [source code](https://github.com/googleapis/java-security-private-ca/blob/master/samples/snippets/cloud-client/src/main/java/privateca/DisableCertificateAuthority.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-security-private-ca&page=editor&open_in_editor=samples/snippets/cloud-client/src/main/java/privateca/DisableCertificateAuthority.java) |
+| Enable Certificate Authority | [source code](https://github.com/googleapis/java-security-private-ca/blob/master/samples/snippets/cloud-client/src/main/java/privateca/EnableCertificateAuthority.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-security-private-ca&page=editor&open_in_editor=samples/snippets/cloud-client/src/main/java/privateca/EnableCertificateAuthority.java) |
+| List Ca Pools | [source code](https://github.com/googleapis/java-security-private-ca/blob/master/samples/snippets/cloud-client/src/main/java/privateca/ListCaPools.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-security-private-ca&page=editor&open_in_editor=samples/snippets/cloud-client/src/main/java/privateca/ListCaPools.java) |
+| List Certificate Authorities | [source code](https://github.com/googleapis/java-security-private-ca/blob/master/samples/snippets/cloud-client/src/main/java/privateca/ListCertificateAuthorities.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-security-private-ca&page=editor&open_in_editor=samples/snippets/cloud-client/src/main/java/privateca/ListCertificateAuthorities.java) |
+| List Certificates | [source code](https://github.com/googleapis/java-security-private-ca/blob/master/samples/snippets/cloud-client/src/main/java/privateca/ListCertificates.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-security-private-ca&page=editor&open_in_editor=samples/snippets/cloud-client/src/main/java/privateca/ListCertificates.java) |
+| Revoke Certificate | [source code](https://github.com/googleapis/java-security-private-ca/blob/master/samples/snippets/cloud-client/src/main/java/privateca/RevokeCertificate.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-security-private-ca&page=editor&open_in_editor=samples/snippets/cloud-client/src/main/java/privateca/RevokeCertificate.java) |
+
+
 
 ## Troubleshooting