Standardize on American English for the Guide

docs/notes/styleguide.rst

@@ -84,6 +84,8 @@ Wrap text lines at 78 characters. Where necessary, lines may exceed 78
 characters, especially if wrapping would make the source text more difficult
 to read.
 
+Use Standard American English, not British English.
+
 Use of the `serial comma <https://en.wikipedia.org/wiki/Serial_comma>`_
 (also known as the Oxford comma) is 100% non-optional. Any attempt to
 submit content with a missing serial comma will result in permanent banishment
@@ -209,4 +211,3 @@ documents or large incomplete sections.
     .. todo::
         Learn the Ultimate Answer to the Ultimate Question
         of Life, The Universe, and Everything
-