chore: regenerate README

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Log from Synthtool

2021-01-06 22:28:28,540 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-document-ai/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-01-06 22:28:29,394 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

Full log will be available here:
https://source.cloud.google.com/results/invocations/f5858ae3-984c-48a2-863b-212ec600a849/targets

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[yoshi-approver]

Rubber stamped PR!

[codecov]

Codecov Report

Merging #309 (4550f14) into master (f9c15c6) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #309   +/-   ##
=========================================
  Coverage     68.58%   68.58%           
  Complexity      122      122           
=========================================
  Files            18       18           
  Lines           850      850           
  Branches          4        4           
=========================================
  Hits            583      583           
  Misses          259      259           
  Partials          8        8           

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