chore: regenerate README (#279)

This PR was generated using Autosynth. 🌈


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

```
2021-04-09 18:40:36,830 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-notification/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-04-09 18:40:38,072 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/22a4c171-3292-4871-a1f4-3d4531c2b3e9/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-notification.git",
-        "sha": "0c776c4071c6645d489833e994b24782c9300a9b"
+        "sha": "28487f3fb98460ee2f4f7a81a64ea2d82b9b2e8f"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "c84c8f156e09702e1c8946bfb9746e6f5892cf27"
+        "sha": "1f5e6bc8dc8e3661ee550905fc070e55e1b6cea1"
       }
     }
   ]

README.md

@@ -8,9 +8,12 @@ Java idiomatic client for [Google Cloud Pub/Sub Notifications for GCS][product-d
 - [Product Documentation][product-docs]
 - [Client Library Documentation][javadocs]
 
+
 > Note: This client is a work-in-progress, and may occasionally
 > make backwards-incompatible changes.
 
+
+
 ## Quickstart