chore: regenerate README (#30)

This PR was generated using Autosynth. 🌈


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

```
2021-04-20 16:03:05,438 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-gkehub/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-04-20 16:03:06,720 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

```
</details>

Full log will be available here:
https://source.cloud.google.com/results/invocations/c0cc90cd-60df-421a-a134-669e0a0c0f79/targets

- [ ] To automatically regenerate this PR, check this box. (May take up to 24 hours.)

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

@@ -0,0 +1,18 @@
+{
+  "sources": [
+    {
+      "git": {
+        "name": ".",
+        "remote": "https://github.com/googleapis/java-gkehub.git",
+        "sha": "be96b8bffa7fee6b9d68988fe14164bfc0ab6b5e"
+      }
+    },
+    {
+      "git": {
+        "name": "synthtool",
+        "remote": "https://github.com/googleapis/synthtool.git",
+        "sha": "ff6b759fcb58f216f62b48d5be0bb85fafbc3bb2"
+      }
+    }
+  ]
+}