Doc: CG: Add guideline for use of 'CSS' prefix in commit messages

Doc: CG: Add guideline for use of 'CSS' prefix in commit messages

[pwm, 2017-07-04 19:28:12]

Please review.  Working on css changes for docs, I realized it wasn't clear to
me, from reading the CG, whether the commit prefix should be 'Doc:' or 'Web:' or
something else. So this clarifies things.

-Paul

[pwm, 2017-07-05 20:05:26]

On second thought...

https://codereview.appspot.com/325970043/diff/1/Documentation/contributor/sou...
File Documentation/contributor/source-code.itexi (right):

https://codereview.appspot.com/325970043/diff/1/Documentation/contributor/sou...
Documentation/contributor/source-code.itexi:1257: affect the website, the
documentation/manuals, or both.
I'm now thinking it would be best to leave out the both case like so:

CSS: Commits that change CSS files should use @qq{Web:@tie{}CSS:@tie{}}
or @qq{Doc:@tie{}CSS:@tie{}} depending on whether they
affect the website or the documentation/manuals.

...since a 'both' commit should probably be split into two commits.  

(Alternatively, if we did want to specify a both case, it should probably
include all three prefixes like "Doc/Web: CSS: " or similar.)

[pwm, 2017-07-08 21:26:47]

Don't mention a 'both' case

[pwm, 2017-07-08 21:30:06]

Round two.  -Paul