Clarify how to install directly from GitHub

Add a textual explaination of why things are the way they are.

docs/contributing/workflow.md

@@ -79,7 +79,11 @@ Generate the documentation for Furo into the `build/docs` folder. This (mostly)
 - Run `nox -s release`
 - Once that command succeeds, you're done!
 
-## Installing directly from the repository (development)
+## Installing directly from GitHub
+
+There are times when you might want to install the in-development version of Furo (mostly for testing that a fix actually does fix things).
+
+Furo cannot be installed directly using pip with the Git repository directly. This is because the Git repository does not contained the compiled CSS/JS. The distributions on PyPI have the compiled assets (because they're platform agnostic and plain text).
 
 ```sh
 # Clone the repository