doc: rerere-options.adoc: link to git-rerere(1)

doc: rerere-options.adoc: link to git-rerere(1)

Five commands include these options. Let’s link to the command so that
the curious user can learn more about what “rerere” is about.

It’s also better to consistently refer to things like
e.g. “git-subcommand(1)” over `git subcommand` or `subcommand`.

Also apply the same treatment to git-add(1).

Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>