Bug 1620078 - Update DevTools docs home page with shorter intro. r=Honza

Differential Revision: https://phabricator.services.mozilla.com/D65426

--HG--
extra : moz-landing-system : lando

devtools/docs/index.rst

@@ -1,16 +1,8 @@
 ========
-DevTools
+Firefox DevTools Contributor Docs
 ========
 
-This collection of linked pages contain design and architectural documents
-for the DevTools implementation in Firefox. DevTools code base lives under
-`devtools` directory.
-
-This `MDN page <https://developer.mozilla.org/en-US/docs/Tools>`__ contains
-information about DevTools features.
-
-This `MDN page <https://www.mozilla.org/en-US/firefox/developer>`__ contains
-information about Developer Edition.
+This is a guide to working on the code for Firefox Developer Tools. If you're looking for help with using the tools, see the `user docs <https://developer.mozilla.org/en-US/docs/Tools>`__. For other ways to get involved, check out our `community site <https://firefox-dev.tools/>`__.
 
 
 Getting Started