Mention how to convert "copies" from gyp to gn in the cookbook.

BUG=none

Review URL: https://codereview.chromium.org/1683123002

Cr-Original-Commit-Position: refs/heads/master@{#374791}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: bf781415f643cacdb62968ef765f83fa12674ac6
1 file changed
tree: aec21f3caaa9ac3f2dc1530b51719bf3e517101b
  1. tools/