user-manual: reorganize public git repo discussion
Helping a couple people set up public repos recently, I wanted to point them at this piece of the user manual, but found it wasn't as helpful as it could be:
- It starts with a big explanation of why you'd want a public repository, not necessary in their case since they already knew why they wanted that. So, separate that out. - It skimps on some of the git-daemon details, and puts the http export information first. Fix that.
Also group all the public repo subsections into a single section, and do some miscellaneous related editing.
Signed-off-by: "J. Bruce Fields" <firstname.lastname@example.org>