docs: clarify that --depth for git-fetch works with newly initialized repos

The original wording sounded as if --depth could only be used to deepen or
shorten the history of existing repos. However, that is not the case. In a
workflow like

    $ git init
    $ git remote add origin https://github.com/git/git.git
    $ git fetch --depth=1

The newly initialized repo is properly created as a shallow repo.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/fetch-options.txt

@@ -8,10 +8,11 @@
 	option old data in `.git/FETCH_HEAD` will be overwritten.
 
 --depth=<depth>::
-	Deepen or shorten the history of a 'shallow' repository created by
-	`git clone` with `--depth=<depth>` option (see linkgit:git-clone[1])
-	to the specified number of commits from the tip of each remote
-	branch history. Tags for the deepened commits are not fetched.
+	Limit fetching to the specified number of commits from the tip of
+	each remote branch history. If fetching to a 'shallow' repository
+	created by `git clone` with `--depth=<depth>` option (see
+	linkgit:git-clone[1]), deepen or shorten the history to the specified
+	number of commits. Tags for the deepened commits are not fetched.
 
 --unshallow::
 	If the source repository is complete, convert a shallow