chore: regenerate README (#501)

This PR was generated using Autosynth. 🌈


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

```
2021-06-02 20:16:30,323 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-document-ai/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-06-02 20:16:31,674 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/a1063312-3def-40f4-ad66-a29288a0abfc/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": "3c2c39baea06ba456302ae2a1f36c7cbfbb2ac0b"
+        "sha": "71506caa78cd34cbca54b8621a03fc45016400fd"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "a2de127f90799cd5bace653b1dcc5dd2ca8b19c9"
+        "sha": "c3e41da0fa256ad7f6b4bc76b9d069dedecdfef4"
       }
     }
   ]

README.md

@@ -28,7 +28,7 @@ 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>0.8.2</version>
+    <version>1.0.0</version>
   </dependency>
 
 ```
@@ -39,7 +39,7 @@ 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>0.8.2</version>
+  <version>1.0.0</version>
 </dependency>
 
 ```
@@ -52,12 +52,12 @@ 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:0.8.2'
+compile 'com.google.cloud:google-cloud-document-ai:1.0.0'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-document-ai" % "0.8.2"
+libraryDependencies += "com.google.cloud" % "google-cloud-document-ai" % "1.0.0"
 ```
 
 ## Authentication