internal/tools/docgen: use go:embed

[mmcloughlin]

No description provided.

[codecov-commenter]

Codecov Report

Merging #123 (33f2f1d) into master (b4dbe78) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #123   +/-   ##
=======================================
  Coverage   73.05%   73.05%           
=======================================
  Files          30       30           
  Lines        1874     1874           
=======================================
  Hits         1369     1369           
  Misses        445      445           
  Partials       60       60           

Flag	Coverage Δ
unittests	73.05% <ø> (ø)

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