chore: regenerate README (#418)

This PR was generated using Autosynth. 🌈


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

```
2021-04-14 00:42:12,634 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-document-ai/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-04-14 00:42:13,896 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

```
</details>

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Author: yoshi-automation

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

@@ -4,14 +4,14 @@
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         "name": ".",
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-        "sha": "ddc286a6cdeeff98469243b8dcf2d978f6239095"
+        "sha": "70f45114f95861dc422df6f7e1e998938c784265"
       }
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       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "0a071b3460344886297a304253bf924aa68ddb7e"
+        "sha": "082e1ca0863b13ada8594fe91845380765da5b70"
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README.md

@@ -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:0.5.0'
+compile 'com.google.cloud:google-cloud-document-ai:0.6.0'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-document-ai" % "0.5.0"
+libraryDependencies += "com.google.cloud" % "google-cloud-document-ai" % "0.6.0"
 ```
 
 ## Authentication