chore: regenerate README

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Log from Synthtool

2021-05-13 13:58:22,446 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-document-ai/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-13 13:58:23,672 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

Full log will be available here:
https://source.cloud.google.com/results/invocations/96bf6bcb-d933-4ccb-ac18-cb107120087c/targets

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[yoshi-approver]

Rubber stamped PR!

[codecov]

Codecov Report

Merging #477 (1a1e699) into master (70efb03) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #477   +/-   ##
=========================================
  Coverage     69.35%   69.35%           
  Complexity      173      173           
=========================================
  Files            24       24           
  Lines          1201     1201           
  Branches          6        6           
=========================================
  Hits            833      833           
  Misses          354      354           
  Partials         14       14           

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