Update docs on how to build and run docserver.
Update docs on how to build and run docserver.

No-Try: true
Docs-Preview: https://skia.org/?cl=90943
Bug: skia:7444
Change-Id: I603e629a2a2a799c9f2ea699cbfb6f6533da327b
Reviewed-on: https://skia-review.googlesource.com/90943
Commit-Queue: Joe Gregorio <b9cf2471ff6d33504cafe8e6f356b732b2cadced@google.com>
Reviewed-by: Ben Wagner <3ef7217be91069877d94f7907ce5479000772cd3@google.com>

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