feat: add .repo-metadata.json, generate docs

[bcoe]

• adds new .repo-metadata.json, used for googleapis.dev doc generation.
• re-generates README.md using template.

[codecov]

Codecov Report

Merging #328 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #328   +/-   ##
=======================================
  Coverage   93.68%   93.68%           
=======================================
  Files           2        2           
  Lines          95       95           
  Branches       21       21           
=======================================
  Hits           89       89           
  Misses          4        4           
  Partials        2        2

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