chore: regenerate README (#446)

This PR was generated using Autosynth. 🌈


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

```
2021-04-21 16:22:42,712 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-document-ai/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-04-21 16:22:43,960 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/5f649939-17c1-40a7-b2bb-ed49faf9ceee/targets

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

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-document-ai.git",
-        "sha": "91be82f3ee91042498fb0a20a6496e965c598bf5"
+        "sha": "464417334090df664b79e94b3cc3111275687d16"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "ff6b759fcb58f216f62b48d5be0bb85fafbc3bb2"
+        "sha": "5a6f30b8bb7672cf237c4f75d5aa96bfba170e7f"
       }
     }
   ]

README.md

@@ -31,7 +31,7 @@ If you are using Maven with [BOM][libraries-bom], add this to your pom.xml file
   <dependency>
     <groupId>com.google.cloud</groupId>
     <artifactId>google-cloud-document-ai</artifactId>
-    <version>0.7.0</version>
+    <version>0.7.1</version>
   </dependency>
 
 ```
@@ -42,7 +42,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-document-ai</artifactId>
-  <version>0.7.0</version>
+  <version>0.7.1</version>
 </dependency>
 
 ```