Added a few examples to git-pull man page.

Added a few examples to git-pull man page.

Clarified and added notes for pull/push refspecs.
Converted to back-ticks for literal text examples.

[jc: Also fixed git-pull description that still talked about its
calling git-resolve or git-octopus (we do not anymore; instead
we just call git-merge).  BTW, I am reasonably impressed by how
well "git-am -3" applied this patch, which had some conflicts
because I've updated the documentation somewhat.]

Signed-off-by: Jon Loeliger <jdl@freescale.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>