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was removed since it's no longer maintained.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the binary installer indicating that it is no longer maintained.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/install/mac.html

@@ -30,6 +30,11 @@ <h3>Xcode Command Line Tools</h3>
   Tools</a>. You can install this via:<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.
+  These installers are no longer linked from here because there are no updates
+  since that version, nor are there plans to provide any.</p>
+
   <h3>Installing git-gui</h3>
   <p>If you would like to install <a href="https://git-scm.com/docs/git-gui/">git-gui</a> and <a href="https://git-scm.com/docs/gitk/">gitk</a>,
   git's commit GUI and interactive history browser, you can do so using <a href="https://brew.sh/">homebrew</a><br>