docs(CONTRIBUTING): define the section hierarchy

Define the recommended section hierarchy in this guide so we have a
quick ref to direct people to. Additionally, keep the link to the Python
Developer's Guide since they have an excellent overview of RST that
people just getting started should consider looking at.

Signed-off-by: Randolph Sapp <[email protected]>

Author: StaticRocket

CONTRIBUTING.md

@@ -164,6 +164,35 @@ in this case:
 replace_b
 ```
 
+### Headings / sections
+
+We are trying to move to the [Python Developer's Guide for
+documenting](https://devguide.python.org/documentation/markup/#sections)
+standard of section hierarchy. This means that section definitions should use
+the following pattern:
+
+```rst
+#########
+Section 1
+#########
+
+*********
+Section 2
+*********
+
+Section 3
+=========
+
+Section 4
+---------
+
+Section 5
+^^^^^^^^^
+
+Section 6
+"""""""""
+```
+
 ## Licensing
 
 ### Community