Update relative links to Linux docs

This is a followup to [1].

[1] https://chromium-review.googlesource.com/c/chromium/src/+/1974901

TBR=sky

Change-Id: I442ffe121378607bdc5e1b16c081b8d66b138955
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1980900
Reviewed-by: Thomas Anderson <[email protected]>
Commit-Queue: Thomas Anderson <[email protected]>
Cr-Commit-Position: refs/heads/master@{#727226}
27 files changed