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
I suggest "edits", since that's what we're actually doing here and it links back to the previous sentence, which is structurally good practice.