chore: regenerate README

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Log from Synthtool

2021-04-14 00:40:21,379 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-secretmanager/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-04-14 00:40:22,613 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

Full log will be available here:
https://source.cloud.google.com/results/invocations/00b24b41-0f89-4c01-87b7-a03737aa8c30/targets

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[codecov]

Codecov Report

Merging #442 (b0434eb) into master (a74fda1) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #442   +/-   ##
=========================================
  Coverage     81.52%   81.52%           
  Complexity      256      256           
=========================================
  Files            12       12           
  Lines          1700     1700           
  Branches         22       22           
=========================================
  Hits           1386     1386           
  Misses          280      280           
  Partials         34       34           

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