also adds comment about updating nginx files during upgrades

* fix code blocks
* Make capitalization of titles consistent - missed some in
https://github.com/gitlabhq/gitlabhq/pull/7576

* Fix some formatting issues
* Make capitalization of titles consistent
* Update image that shows how to select branch

The following error is encountered during the installation of the rugged gem:

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    /usr/bin/ruby2.1 extconf.rb
    checking for cmake... no
    ERROR: CMake is required to build Rugged.
    *** extconf.rb failed ***

Update `curl` commands to follow redirects (see
http://curl.haxx.se/docs/manpage.html#-L). Current `curl` commands will
return unexpected results if the requested content has been moved and is
returning information about where it has been moved to. Including the
`-L` option tells `curl` to follow the redirect so the file can be
correctly acquired.

Further changes

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Just a minor fix ;)

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Ruby version updated so it doesn't have the readline bug https://www.ruby-lang.org/en/news/2014/05/09/ruby-2-0-0-p481-is-released/.