We want to require use of the Windows 10 SDK in ANGLE - Chrome
already uses a newer SDK.
A new gyp feature added by munyirik@microsoft.com allows us to use
the latest Win 10 SDK installed on the system, irrespective of the
minor version number.
Also update the docs.
BUG=angleproject:1943
Change-Id: Iaafbba858fb7565ab09672eadc403dbb8abab3dd
Reviewed-on: https://chromium-review.googlesource.com/458516
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
