WebSockets: Link to design docs from README.md

There are numerous WebSocket-related design docs, some of which contain
useful information. Add links to the design docs to the README.md files
for WebSockets, together with some brief context about how current they
are.

Change-Id: Ibd5c4b147c01bed079b0f09934cc5b67684c1547
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1508473
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638938}
2 files changed