Add a link to a basic command-line primer to the Getting Started page

[kadamwhite]

Grunt got called out (in a friendly way) at WordCamp Boston for making the assumption in its docs that people know command-line basics. While this is not an atrociously unsafe assumption, there's definitely an audience of beginning developers who are less familiar with the command line, across both Windows and OSX platforms. We ought to make a note in getting started that Grunt is first and foremost a CLI, and link to a quick primer on how the command line works in different environments.

I'm vetting primers now, but I'm not sure where the content itself actually lives in this repo so I'm not yet able to PR.

[kadamwhite]

Aha! Found the site content in grunt-docs repo. Will look for a good CLI tutorial and PR.

[kadamwhite]

Reopening to use this to track whether the Grunt team approves the instinct, and to document what resource would be best to link, if so

[cowboy]

I'd love better docs around this. I wrote the Getting Started guide, but I already know CLI basics.

[kadamwhite]

@cowboy I'm checking these videos out on @ashleygwilliams' recommendation: http://commandlinepoweruser.com/ If they're good I'll make a PR against the docs repo to add a link to them