Explicitly say doxygen comments use triple-slash

[probinson]

Summary

I've had a couple of questions about this and thought maybe the coding standard
should be more explicit about it. Advice from the group-mind welcome.

[probinson]

Too obvious/trivial to need review.

docs/CodingStandards.rst

.. note::
     on the first line, along with a very short description of the purpose of the
     file.  This is important when printing out code and flipping though lots of
     pages.
 
 The next section in the file is a concise note that defines the license that the
 file is released under.  This makes it perfectly clear what terms the source
 code can be distributed under and should not be modified in any way.
 
-The main body is a ``doxygen`` comment describing the purpose of the file.  It
+The main body is a ``doxygen`` comment (identified by the ``///`` comment
+marker instead of the usual ``//``) describing the purpose of the file.  It
 should have a ``\brief`` command that describes the file in one or two
 sentences.  Any additional information should be separated by a blank line.  If
 an algorithm is being implemented or something tricky is going on, a reference
 to the paper where it is published should be included, as well as any notes or
 *gotchas* in the code to watch out for.
 
 Class overviews
 """""""""""""""

 figure out how to use your interfaces without reading the code itself.
 
 Good things to talk about here are what happens when something unexpected
 happens: does the method return null?  Abort?  Format your hard disk?
 
 Comment Formatting
 ^^^^^^^^^^^^^^^^^^
 
-In general, prefer C++ style (``//``) comments.  They take less space, require
+In general, prefer C++ style comments (``//`` for normal comments, ``///`` for
+``doxygen`` documentation comments).  They take less space, require
 less typing, don't have nesting problems, etc.  There are a few cases when it is
 useful to use C style (``/* */``) comments however:
 
 #. When writing C code: Obviously if you are writing C code, use C style
    comments.
 
 #. When writing a header file that may be ``#include``\d by a C source file.