git-submodule.txt: Clarify 'init' and 'add' subcommands.

Describe how 'add' sets the submodule's logical name, which is used in
the configuration entry names.

Clarify that 'init' only sets up the configuration entries for
submodules that have already been added elsewhere.  Describe that
<path> arguments limit the submodules that are configured.
Signed-off-by: NDale Worley <worley@ariadne.com>
Acked-by: NJens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-submodule.txt

@@ -77,6 +77,8 @@ argument <path> is the relative location for the cloned submodule
 to exist in the superproject. If <path> is not given, the
 "humanish" part of the source repository is used ("repo" for
 "/path/to/repo.git" and "foo" for "host.xz:foo/.git").
+The <path> is also used as the submodule's logical name in its
+configuration entries unless `--name` is used to specify a logical name.
 +
 <repository> is the URL of the new submodule's origin repository.
 This may be either an absolute URL, or (if it begins with ./
@@ -124,8 +126,10 @@ linkgit:git-status[1] and linkgit:git-diff[1] will provide that information
 too (and can also report changes to a submodule's work tree).
 
 init::
-	Initialize the submodules, i.e. register each submodule name
-	and url found in .gitmodules into .git/config.
+	Initialize the submodules recorded in the index (which were
+	added and committed elsewhere) by copying submodule
+	names and urls from .gitmodules to .git/config.
+	Optional <path> arguments limit which submodules will be initialized.
 	It will also copy the value of `submodule.$name.update` into
 	.git/config.
 	The key used in .git/config is `submodule.$name.url`.