Add /docs/README.md
Add /docs/README.md

Add /docs/README.md with a link to the style guide

R=andybons@chromium.org
BUG=528673

Review URL: https://codereview.chromium.org/1342543005

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#348625}

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