Link to most recent DevDocs when installing from Master Source #15610
Description
Bug report
Bug summary
Installing from source location references older documentation that doesn't align with the current master branch. We should link to the latest development documentation from:
https://matplotlib.org/3.1.1/users/installing.html#installing-from-source
pointing to:
https://matplotlib.org/devdocs/users/installing.html#installing-from-source