added MakeFromYUVATextures to docs

added MakeFromYUVATextures to docs

TBR=jvanverth@google.com
NOTRY=true
Docs-Preview: https://skia.org/?cl=166623
Bug: skia:
Change-Id: Iec7769e289f91432e2ab1e550376947b897ff186
Reviewed-on: https://skia-review.googlesource.com/c/166623
Commit-Queue: Cary Clark <caryclark@skia.org>
Auto-Submit: Cary Clark <caryclark@skia.org>
Reviewed-by: Cary Clark <caryclark@skia.org>
2 files changed