downloads/mac: re add binary installer

In commit 54175ad the binary installer
was removed since it's no longer maintained. Now there are still a lot
of references to that page mentioning the binary installer, for example
Pro Git book[0] or Stack Overflow[1]. To reduce confusion this re adds
the binary installer indicating that it is no longer maintained.

[0]: https://git-scm.com/book/en/v2/Getting-Started-Installing-Git
[1]: https://stackoverflow.com/a/70764034

Author: kerhac

content/downloads/mac.html

@@ -28,6 +28,10 @@ <h3>Xcode Command Line Tools</h3>
   Tools</a>.<br>
   <code>$ xcode-select --install</code></p>
 
+  <h3>Binary installer</h3>
+  <p>Tim Harper provided an installer for Git until version 2.33.0 / 2021. This
+  project was archived in favor of Xcode Command Line Tools.</p>
+
   <h3>Building from Source</h3>
   <p>If you prefer to build from source, you can find tarballs
   <a href="https://www.kernel.org/pub/software/scm/git/">on kernel.org</a>.