NPM installs globally whenever you use the -g switch, so you need not worry about the location. Just use sudo if you don’t have the requisite privileges.
When NPM had installed everything you will need to double check bower has installed dependencies and then run you grunt command of choice (again look in the README).
Please stop telling to read README, I followed everything there and still getting this error.
I hope someone could help me with this. Thanks in advance!