doc branch: provide examples for listing remote tracking branches

doc branch: provide examples for listing remote tracking branches

The availability of these pattern selections is not obvious from
the man pages, as per mail thread <87lfz3vcbt.fsf@evledraar.gmail.com>.

Provide examples.

Re-order the `git branch` synopsis to emphasise the `--list <pattern>`
pairing. Also expand and reposition the `all/remotes` options.

Split the over-long description into three parts so that the <pattern>
description can be seen.

Clarify that the `all/remotes` options require the --list if patterns
are to be used.

Add examples of listing remote tracking branches that match a pattern,
including `git for-each-ref` which has more options.

Improve the -a/-r warning message. The message confused this author
as the combined -a and -r options had not been given, though a pattern
had. Specifically guide the user that maybe they needed the --list
option to enable a remote branch pattern selection.

Signed-off-by: Philip Oakley <philipoakley@iee.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>