Add missing devdocs subproject

Author: QuLogic

Caddyfile

@@ -47,6 +47,7 @@
 	import subproject basemap
 	import subproject cheatsheets
 	import subproject cycler
+	import subproject devdocs
 	import subproject governance
 	import subproject matplotblog
 	import subproject mpl-altair

README.md

@@ -21,6 +21,7 @@ related projects are also exposed as toplevel directories:
 * [basemap](https://github.com/matplotlib/basemap)
 * [cheatsheets](https://github.com/matplotlib/cheatsheets)
 * [cycler](https://github.com/matplotlib/cycler)
+* [devdocs](https://github.com/matplotlib/devdocs)
 * [governance](https://github.com/matplotlib/governance)
 * [matplotblog](https://github.com/matplotlib/matplotblog)
 * [mpl-altair](https://github.com/matplotlib/mpl-altair)