compiler_wrapper: Updated instructions for updating the wrapper

This change adds some more details on how to test and commit
changes to the compiler wrapper.

BUG=None
TEST=Followed the steps locally to verify that they work.

Change-Id: I5a3d644e92fd94ed3792a59a30f39db08053390d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/2305371
Commit-Queue: Bob Haarman <inglorion@chromium.org>
Tested-by: Bob Haarman <inglorion@chromium.org>
Reviewed-by: George Burgess <gbiv@chromium.org>
Reviewed-by: Jian Cai <jiancai@google.com>
1 file changed