Bug 1687980: Make Windows quickstart docs more concise r=mhoye,sylves…

…tre,andi

* Puts the docs in order, so that contributors aren't jumping to the
  middle of the page to install system tools, then back to the top to
  clone Firefox.
* Removes docs on MacPorts since it's being removed in bug 1688263.
* Removes step to manually install brew packages since that happens
   automatically in bootstrap now.
* Simplifies mercurial installation docs
* Removes unnecessary mozconfig-tweaking instructions
* Removes almost-always-unnecessary DEFINE and troubleshooting
  information.

Differential Revision: https://phabricator.services.mozilla.com/D102974

browser/installer/windows/docs/InstallerBuild.rst

@@ -31,6 +31,13 @@ You can build installers (and the entire application) with official branding by
 Build process
 -------------
 
+.. note::
+
+   If you intend to distribute your build to others, you'll want to add
+   ``export WIN32_REDIST_DIR=<CRT_LOCATION>`` in your ``mozconfig``. The CRT location
+   will vary depending on your Visual Studio version. At the time of writing, this would look like:
+   ``export WIN32_REDIST_DIR="/c/Program Files (x86)/Microsoft Visual Studio/2019/Community/VC/Redist/MSVC/14.28.29325/x86/Microsoft.VC142.CRT"``.
+
 Both the full and stub installers are built through a similar process, which is summarized here along with references to the relevant bits of code.
 
 Most of this procedure is done in `makensis.mk <https://searchfox.org/mozilla-central/source/toolkit/mozapps/installer/windows/nsis/makensis.mk>`_ and in the `mach repackage <https://searchfox.org/mozilla-central/rev/2b9779c59390ecc47be7a70d99753653d8eb5afc/python/mozbuild/mozbuild/mach_commands.py#2166>`_ command.