Documentation: describe "-f/-t/-m" options to "git-remote add"

Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-remote.txt

@@ -31,6 +31,19 @@ subcommands are available to perform operations on the remotes.
 Adds a remote named <name> for the repository at
 <url>.  The command `git fetch <name>` can then be used to create and
 update remote-tracking branches <name>/<branch>.
++
+With `-f` option, `git fetch <name>` is run immediately after
+the remote information is set up.
++
+With `-t <branch>` option, instead of the default glob
+refspec for the remote to track all branches under
+`$GIT_DIR/remotes/<name>/`, a refspec to track only `<branch>`
+is created.  You can give more than one `-t <branch>` to track
+multiple branche without grabbing all branches.
++
+With `-m <master>` option, `$GIT_DIR/remotes/<name>/HEAD` is set
+up to point at remote's `<master>` branch instead of whatever
+branch the `HEAD` at the remote repository actually points at.
 
 'show'::