Adds notes about privileges.

README.md

@@ -72,6 +72,11 @@ From the command line:
 
 When completed, you'll be able to run the various Grunt commands provided from the command line.
 
+**N.B.** 
+You will need write permission to the global npm directory to install `grunt-cli` and `bower`. You will also likely have to be using an elevated terminal or prefix the command with `sudo`, i.e., `sudo install -g grunt-cli bower`. 
+
+We also advise against running as root user. NPM deliberately uses limited privileges when executing certain commands such as those included in the Roots post-install process, and when this happens to the root user, any file system objects that are not expressly writable by the root user will fail to write during the execution of the command. These might include directories such as `/var/www` or `/home/someotheruser`. If you're running as root and have problems, don't say we didn't warn you.
+
 ### Available Grunt commands
 
 * `grunt dev` — Compile LESS to CSS, concatenate and validate JS