refspec for the remote to track all branches under
`$GIT_DIR/remotes/<name>/`, a refspec to track only `<branch>`
is created. You can give more than one `-t <branch>` to track
-multiple branche without grabbing all branches.
+multiple branches without grabbing all branches.
+
With `-m <master>` option, `$GIT_DIR/remotes/<name>/HEAD` is set
up to point at remote's `<master>` branch instead of whatever