Clarify doc comments to document the meaning of 'hairline'.

The concept of "hairline" width is well understood by team members,
but was not actually documented anywhere in the code. Added a bit of
explanatory text to the doc comments.

Change-Id: I51c39e2e644b8353afbdb8bdda32263796d7e951
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/290676
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed