Drop this "metacity-nothing-theme" directory into ~/themes and rename it to
"nothing", so that you have the following path to the theme xml file:

~/.themes/nothing/metacity-1/metacity-theme-1.xml

Or just run the following two commands:

$ mkdir -p ~/.themes/nothing/metacity-1
$ wget http://github.com/mackstann/metacity-nothing-theme/\
raw/master/metacity-1/metacity-theme-1.xml -O \
~/.themes/nothing/metacity-1/metacity-theme-1.xml