Documentation: improve "add", "pull" and "format-patch" examples

Documentation: improve "add", "pull" and "format-patch" examples

Before this patch in "git-add.txt" and "git-format-patch.txt", the
commands used in the examples were "git-CMD" instead of "git CMD".
This patch fixes that.

In "git-pull.txt" only the last example had the code sample in an
asciidoc "Listing Block", and in the other two files, none.
This patch fixes that by putting all code samples in listing
blocks.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>