chore: regenerate README (#138)

This PR was generated using Autosynth. 🌈


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

```
2021-06-02 20:14:12,185 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-pubsublite-kafka/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-06-02 20:14:13,424 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/56db0cdc-6b57-461f-9412-c55b9ba97aae/targets

- [ ] To automatically regenerate this PR, check this box. (May take up to 24 hours.)

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-pubsublite-kafka.git",
-        "sha": "2445761bb78a12082ae0aba7f22f969bbc91042e"
+        "sha": "6d051459d82db368892be72102ec5ae2d6738493"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "2e7bd5cc66a3f0b90ce1c150eb35c89eeb9872d6"
+        "sha": "c3e41da0fa256ad7f6b4bc76b9d069dedecdfef4"
       }
     }
   ]

README.md

@@ -63,6 +63,9 @@ be implemented using Pub/Sub Lite as a backend. The key differences are:
 - Producers operate on a single topic, and Consumers on a single subscription.
 - ProducerRecord may not specify partition explicitly.
 - Consumers may not dynamically create consumer groups (subscriptions).
+- `Consumer.offsetsForTimes` and `Consumer.endOffsets` will raise an
+  exception.
+
 
 
 #### Publishing messages