add some more to CONTRIBUTING.md

Questions for others involved in cli support -

- is there a npm-support (vs npm general) irc channel?  Do we want to send people to the #npm channel? Should we create a new channel? Can we recruit people who want to help and get them to come hang out on a new channel?

- how's the language in this CONTRIBUTING.md ? I'm aiming for a less-technical level, since it feels like a lot of the people who create npm support requests these days are novice developers, or people who are running into npm issues 'on the way' to trying to do something else with npm -- install ember-cli, for example, or install a nodeschool.io module.  I'm also trying to be mindful of the ideas Kathy Sierra lays out here -- http://www.mindtheproduct.com/2014/09/kathy-sierra-building-badass-users/  (around 40:00) -- in particular, anybody who is having trouble with npm is already in a bad place, frustrated, etc., and we should try to reassure them that this is "typical & temporary"

comments/thoughts ? /cc @faiq @iarna @othiym23 @KenanY 
I'd actually like to draw a distinction between support requests (belong here) and bug reports / feature requests / pull requests (belong on npm/npm).

So something like --

If you are not sure where to create an issue, create it here.

If you have a repro set, or have written a failing test, or have made other changes to your own fork of `npm`, then please create a pull request against the `npm/npm` project.