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>

Documentation/rerere-options.adoc

@@ -4,6 +4,6 @@
 	the current conflict to update the files in the working
 	tree, allow it to also update the index with the result of
 	resolution.  `--no-rerere-autoupdate` is a good way to
-	double-check what `rerere` did and catch potential
+	double-check what linkgit:git-rerere[1] did and catch potential
 	mismerges, before committing the result to the index with a
-	separate `git add`.
+	separate linkgit:git-add[1].