Mention the mkdocs.yml file for adding new documents

and move the complicated discussion about branches lower down,
hopefully most won't need to know

Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au>

@fredlf @jamtur01 @ostezer
Suggestion:

.com) documentation may .. > .com) documentation (from always up-to-date `master`) may

(or something)