Improve docs on how to run NOT as a global module

[mhulse]

This could be useful to document for those that don't want to run npm link:

# Use as a global module:
$ npm link
$ boilerplate -d path/to/a/directory/

# Otherwise:
$ npm install
$ node . -d path/to/a/directory/

Also good to note, maybe, that there is npm start which returns the help by default. One could modify this to run node . and then npm start -- -d path/to/a/directory/; this is a bit more syntax than the “otherwise” listed above.