Update lint target documentation.

  o Change table-of-contents depth from 2 to 1.
  o {topic}/index.rst can render sub-index content.

  o Document doc8 lint to reflect latest targets in repo:onf-make.
  o Update header tokens to render w/o the need for (TOC) table-of-contents formatting.

See Also
  o https://docs.voltha.org/master/howto/
  o https://docs.voltha.org/master/howto/code/linting.html

Change-Id: I684837c457c42c184620b87ad639c47f43061189
3 files changed