Mention Homebrew install instructions (#242)

* Mention Homebrew install instructions

* Add "community-supported distribution" section

Emphasize that Homebrew support is unofficial

README.md

@@ -138,6 +138,17 @@ cd flintrock/
 You'll probably want to add the location of the Flintrock executable to your `PATH` so that you
 can invoke it from any directory.
 
+### Community-supported distributions
+
+Flintrock may be available in your favorite package manager!
+These packages are not supported by the core contributors and may be out of date.
+Please reach out to these communities directly if you have trouble using them to install flintrock.
+
+These include:
+
+ * [Homebrew](https://brew.sh): `brew install flintrock`
+
+
 ### Development version
 
 If you like living on the edge, install the development version of Flintrock: