chore: regenerate README (#403)

This PR was generated using Autosynth. 🌈


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

```
2021-06-09 18:18:29,846 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-aiplatform/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-06-09 18:18:31,142 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

```
</details>

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https://source.cloud.google.com/results/invocations/4613eef6-f07f-45ca-aac2-b743b9dbc773/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-aiplatform.git",
-        "sha": "0d30f840fa9ab7215ea6e58e4f6b8fc8bdde8fd2"
+        "sha": "348a87fb714f7be84befe57d461857b0409a804f"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "2430f8d90ed8a508e8422a3a7191e656d5a6bf53"
+        "sha": "740366bbb9a7e0f4b77fc75dc26be1d3a376c3e0"
       }
     }
   ]

README.md

@@ -8,9 +8,6 @@ Java idiomatic client for [Vertex AI][product-docs].
 - [Product Documentation][product-docs]
 - [Client Library Documentation][javadocs]
 
-> Note: This client is a work-in-progress, and may occasionally
-> make backwards-incompatible changes.
-
 ## Quickstart
 
 If you are using Maven with [BOM][libraries-bom], add this to your pom.xml file
@@ -195,9 +192,6 @@ Java 7 or above is required for using this client.
 This library follows [Semantic Versioning](http://semver.org/).
 
 
-It is currently in major version zero (``0.y.z``), which means that anything may change at any time
-and the public API should not be considered stable.
-
 ## Contributing
 
 
@@ -237,7 +231,7 @@ Java is a registered trademark of Oracle and/or its affiliates.
 [kokoro-badge-link-4]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-aiplatform/java8-win.html
 [kokoro-badge-image-5]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-aiplatform/java11.svg
 [kokoro-badge-link-5]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-aiplatform/java11.html
-[stability-image]: https://img.shields.io/badge/stability-beta-yellow
+[stability-image]: https://img.shields.io/badge/stability-ga-green
 [maven-version-image]: https://img.shields.io/maven-central/v/com.google.cloud/google-cloud-aiplatform.svg
 [maven-version-link]: https://search.maven.org/search?q=g:com.google.cloud%20AND%20a:google-cloud-aiplatform&core=gav
 [authentication]: https://github.com/googleapis/google-cloud-java#authentication