chore: regenerate README

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Log from Synthtool

2021-04-12 14:26:39,038 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-pubsub/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-04-12 14:26:40,279 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

Full log will be available here:
https://source.cloud.google.com/results/invocations/2feb5ddc-6ec1-4c79-941c-350ce6abbc83/targets

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[yoshi-approver]

Rubber stamped PR!

[codecov]

Codecov Report

Merging #596 (7cc0cc3) into master (972a286) will decrease coverage by 0.70%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #596      +/-   ##
============================================
- Coverage     78.88%   78.18%   -0.71%     
  Complexity      379      379              
============================================
  Files            27       27              
  Lines          3420     3420              
  Branches        171      169       -2     
============================================
- Hits           2698     2674      -24     
- Misses          650      653       +3     
- Partials         72       93      +21     

Impacted Files	Coverage Δ	Complexity Δ
...oogle/cloud/pubsub/v1/SubscriptionAdminClient.java	57.65% <0.00%> (-5.41%)	52.00% <0.00%> (ø%)
...om/google/cloud/pubsub/v1/SchemaServiceClient.java	57.47% <0.00%> (-3.45%)	20.00% <0.00%> (ø%)
...gle/cloud/pubsub/v1/SequentialExecutorService.java	87.77% <0.00%> (-3.34%)	0.00% <0.00%> (ø%)
...a/com/google/cloud/pubsub/v1/TopicAdminClient.java	56.64% <0.00%> (-2.32%)	34.00% <0.00%> (ø%)
...ain/java/com/google/cloud/pubsub/v1/Publisher.java	87.16% <0.00%> (-0.49%)	47.00% <0.00%> (ø%)

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