chore: regenerate README

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Log from Synthtool

2020-10-16 00:13:13,664 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-firestore/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working directory clean
2020-10-16 00:13:14,625 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

Full log will be available here:
https://source.cloud.google.com/results/invocations/04362563-1f12-4d2e-9128-b888e8798e2a/targets

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[codecov]

Codecov Report

Merging #422 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #422   +/-   ##
=========================================
  Coverage     72.82%   72.82%           
+ Complexity     1067     1058    -9     
=========================================
  Files            64       64           
  Lines          5611     5611           
  Branches        695      697    +2     
=========================================
  Hits           4086     4086           
  Misses         1312     1312           
  Partials        213      213           

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