Add typeface to shaper md

Change-Id: I5c1122a10be320e877b2adba992edb58e3ca1f9e
No-Try: true
Docs-Preview: https://skia.org/?cl=444981
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/444981
Reviewed-by: Florin Malita <fmalita@google.com>
Commit-Queue: Mike Reed <reed@google.com>