(DOCSP-7298): Add LeafyGreen UI link.

Author: Tony Sansone

conf.py

@@ -106,7 +106,8 @@ def has(self, *args):
     'sphinx-rst' : ('https://www.sphinx-doc.org/en/master/usage/restructuredtext%s', ''),
     'sphinx' : ('https://www.sphinx-doc.org/en/master%s', ''),
     'rst' : ('http://docutils.sourceforge.net/docs/ref/rst%s',''),
-    'cc' : ('https://creativecommons.org/licenses%s','')
+    'cc' : ('https://creativecommons.org/licenses%s',''),
+    'gh' : ('https://github.com%s','')
 }
 
 ## add `extlinks` for each published version.

source/style-guide.txt

@@ -61,6 +61,10 @@ MongoDB external and internal customers.
    MongoDB products. You can use these basic guidelines,
    however, when writing release notes for any product or service.
 
+:gh:`User Interface Guidelines </mongodb/leafygreen-ui>`
+   Provides specifications for the user interface of MongoDB web and
+   desktop applications. The components can be viewed
+   `online <https://mongodb.github.io/leafygreen-ui/>`__
 
 .. cssclass:: hidden