Trouble following Usage instructions

[box293]

I tried following the usage instructions but the git subtree add command fails.

troylea@office_itx_gentoo /tmp $ git init test
Initialized empty Git repository in /tmp/test/.git/
troylea@office_itx_gentoo /tmp $ cd test/
troylea@office_itx_gentoo /tmp/test $ git remote add autoconf-macros [email protected]:NagiosEnterprises/autoconf-macros
troylea@office_itx_gentoo /tmp/test $ ls -la
total 12
drwxr-xr-x  3 troylea troylea 4096 Feb  8 11:19 .
drwxrwxrwt 10 root    root    4096 Feb  8 11:19 ..
drwxr-xr-x  6 troylea troylea 4096 Feb  8 11:20 .git
troylea@office_itx_gentoo /tmp/test $  git subtree add --prefix=macros/ autoconf-macros master
fatal: ambiguous argument 'HEAD': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'
Working tree has modifications.  Cannot add.