Differential Revision: https://phabricator.services.mozilla.com/D58338

--HG--
rename : tools/docs/docs/contribute/mozilla_source_code_directory_structure.rst => docs/contributing/directory_structure.rst
rename : tools/docs/docs/contribute/how_to_contribute_firefox.rst => docs/contributing/how_to_contribute_firefox.rst
rename : tools/docs/docs/adding-documentation.rst => tools/moztreedocs/docs/adding-documentation.rst
rename : tools/docs/docs/index.rst => tools/moztreedocs/docs/index.rst
rename : tools/docs/docs/mdn-import.rst => tools/moztreedocs/docs/mdn-import.rst
extra : moz-landing-system : lando