Add header file installation tips for building skia

No-Try: true
Docs-Preview: https://skia.org/?cl=105540
Bug: skia:
Change-Id: I5d83eeb4ba7faf9c2964c91d39d51b3a8efd14a4
Reviewed-on: https://skia-review.googlesource.com/105540
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
2 files changed