Add comment on TBR'ing GN bootstrap changes.

It should be clear that people can TBR certain types of updates to the
bootstrap script.

Review-Url: https://codereview.chromium.org/2776313004
Cr-Original-Commit-Position: refs/heads/master@{#460444}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: b17ee3d6890cf542ff39366a5f6579d540314829
1 file changed
tree: b32e068e5b3abaf3397c95303f3fc3607b6a0b11
  1. tools/