chore: regenerate README (#477)

This PR was generated using Autosynth. 🌈


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

```
2021-05-13 13:58:22,446 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-document-ai/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-13 13:58:23,672 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/96bf6bcb-d933-4ccb-ac18-cb107120087c/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-document-ai.git",
-        "sha": "9a0de3c91e753bf7be699267ee803debc17aae4f"
+        "sha": "70efb031d434e11b44ac44528e12a86d3a7e1ba7"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "6726988c677bb78385868bfc48dbfa2fe981d44a"
+        "sha": "bd8281a06cc7f84906e04d4843c1d3d386a980cd"
       }
     }
   ]

README.md

@@ -20,7 +20,7 @@ If you are using Maven with [BOM][libraries-bom], add this to your pom.xml file
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>libraries-bom</artifactId>
-      <version>20.2.0</version>
+      <version>20.3.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>
@@ -55,12 +55,12 @@ compile 'com.google.cloud:google-cloud-document-ai'
 ```
 If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-document-ai:0.8.0'
+compile 'com.google.cloud:google-cloud-document-ai:0.8.1'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-document-ai" % "0.8.0"
+libraryDependencies += "com.google.cloud" % "google-cloud-document-ai" % "0.8.1"
 ```
 
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