Add a Quick Readme to //ui/views

Change-Id: Id5e17a6efcfe809f18efc0c0346e939e45dc5993
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2414620
Commit-Queue: Robert Liao <robliao@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Auto-Submit: Robert Liao <robliao@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807595}

ui/views/README.md

+# Views UI Toolkit
+The Views UI Toolkit (aka Views) powers the UI on Windows, Mac, Linux, and
+ChromeOS.
+
+# Documentation
+Find the documentation for Views at the [Chromium UI Platform Doc site](/docs/ui/index.md).
+
+# Contact
+Need to contact the team?
+E-mail [views@chromium.org](mailto:views@chromium.org).