chore: regenerate README (#309)

This PR was generated using Autosynth. 🌈


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

```
2021-01-06 22:28:28,540 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-document-ai/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-01-06 22:28:29,394 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/f5858ae3-984c-48a2-863b-212ec600a849/targets

- [ ] To automatically regenerate this PR, check this box.

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-document-ai.git",
-        "sha": "8310f918449e29a8af4980231e6c681af59c4818"
+        "sha": "f9c15c67b3eb5770d4d6be1409116bbe7b02705e"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "996775eca5fd934edac3c2ae34b80ff0395b1717"
+        "sha": "a3e990f3545dc8ccd384a75d20ce9cb185ca6a28"
       }
     }
   ]

README.md

@@ -47,13 +47,20 @@ If you are using Maven without BOM, add this to your dependencies:
 
 ```
 
-If you are using Gradle, add this to your dependencies
+If you are using Gradle 5.x or later, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-document-ai:0.3.6'
+implementation platform('com.google.cloud:libraries-bom:16.2.0')
+
+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:0.3.7'
 ```
+
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-document-ai" % "0.3.6"
+libraryDependencies += "com.google.cloud" % "google-cloud-document-ai" % "0.3.7"
 ```
 
 ## Authentication