Send developers straight to the text relocation docs.

It's been years since we allowed text relocations, but I had a developer
ask me how to fix them at last week's O Developer Day. They'd never seen
our docs, so let's try to fix that for anyone else who's still confused...

Bug: N/A
Test: builds
Change-Id: I9202a7b0a3f024041b646c43c87585f4fab22d09