Bug 1966432 - Modernise Firefox's README, DONTBUILD r=sylvestre

Differential Revision: https://phabricator.services.mozilla.com/D249419

README.md

@@ -0,0 +1,18 @@
+![Firefox Browser](./docs/readme/readme-banner.svg)
+
+[Firefox](https://firefox.com/) is a fast, reliable and private web browser from the non-profit [Mozilla organization](https://mozilla.org/).
+
+### Contributing
+
+To learn how to contribute to Firefox read the [Firefox Contributors' Quick Reference document](https://firefox-source-docs.mozilla.org/contributing/contribution_quickref.html).
+
+We use [bugzilla.mozilla.org](https://bugzilla.mozilla.org/) as our issue tracker, please file bugs there.
+
+### Resources
+
+* [Firefox Source Docs](https://firefox-source-docs.mozilla.org/) is our primary documentation repository
+* Nightly development builds can be downloaded from [Firefox Nightly page](https://www.mozilla.org/firefox/channel/desktop/#nightly)
+
+If you have a question about developing Firefox, and can't find the solution
+on [Firefox Source Docs](https://firefox-source-docs.mozilla.org/), you can try asking your question on Matrix at
+chat.mozilla.org in the [Introduction channel](https://chat.mozilla.org/#/room/#introduction:mozilla.org).

README.txt

@@ -1,21 +0,0 @@
-An explanation of the Firefox Source Code Directory Structure and links to
-project pages with documentation can be found at:
-
-    https://firefox-source-docs.mozilla.org/contributing/directory_structure.html
-
-For information on how to build Firefox from the source code and create the patch see:
-
-    https://firefox-source-docs.mozilla.org/contributing/contribution_quickref.html
-
-If you have a question about developing Firefox, and can't find the solution
-on https://firefox-source-docs.mozilla.org/, you can try asking your question on Matrix at chat.mozilla.org in `Introduction` (https://chat.mozilla.org/#/room/#introduction:mozilla.org) channel.
-
-
-Nightly development builds can be downloaded from:
-
-    https://archive.mozilla.org/pub/firefox/nightly/latest-mozilla-central/
-            - or -
-    https://www.mozilla.org/firefox/channel/desktop/#nightly
-
-Keep in mind that nightly builds, which are used by Firefox developers for
-testing, may be buggy.

moz.build

@@ -52,7 +52,7 @@ with Files("**/l10n.toml"):
     BUG_COMPONENT = ("Core", "Localization")
     FINAL = True
 
-with Files("README.txt"):
+with Files("README.md"):
     BUG_COMPONENT = ("Core", "General")
 
 with Files("SECURITY.md"):