Update AutoBuilder docs to use syntax highlighting
Update AutoBuilder docs to use syntax highlighting

This improves the readability of the page.

Fixes #1323

COPYBARA_INTEGRATE_REVIEW=https://github.com/google/auto/pull/1323 from mgp:patch-1 5398860745c546e3852b1117c7d72d6816fdd2ea
PiperOrigin-RevId: 450429526

eamonnmcmanus/auto,eamonnmcmanus/auto,google/auto,eamonnmcmanus/auto,google/auto,google/auto