chore: regenerate README (#297)

This PR was generated using Autosynth. 🌈


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

```
2021-04-09 16:48:33,773 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-recommendations-ai/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-04-09 16:48:34,983 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/593330bd-c05f-4ae9-8c09-5b29c70db52b/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-recommendations-ai.git",
-        "sha": "fbb42377160890aa67fe898b12777f555f2e8639"
+        "sha": "33fcdb666c58dd128d23ac41317b210182bf0060"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "c84c8f156e09702e1c8946bfb9746e6f5892cf27"
+        "sha": "5b0e1592dd7d70b485e157ea4b3eb1704ecbd015"
       }
     }
   ]

README.md

@@ -8,8 +8,10 @@ Java idiomatic client for [Recommendations AI][product-docs].
 - [Product Documentation][product-docs]
 - [Client Library Documentation][javadocs]
 
-> Note: This client is a work-in-progress, and may occasionally
+> This repo contains beta version of Recommendations AI and may occasionally
 > make backwards-incompatible changes.
+> Recommendations AI is now GA and available as
+> [Google Cloud Retail](https://github.com/googleapis/java-retail)
 
 ## Quickstart