Update README.md

Fix #1

Author: clyne

README.md

@@ -1,7 +1,7 @@
 # VAST Hugo Website
 
 This repository holds the NCAR VAST section website deployed with GitHub Pages.
-See the [Contributor Guide](CONTRIBUTING) for how to add to this site.
+See the [Contributor Guide](CONTRIBUTING.md) for how to add to this site.
 
 This Hugo site is based on the DART GitHub Pages website, which can be found
 [here](https://github.com/NCAR/dart-web-ref).