Update CONTRIBUTING.md to be more comprehensive

[sarina]

Comments welcome from ANYONE! This pull request updates our main CONTRIBUTING.md file to be more clear about what potential open source contributors to edx-platform need to do in order to contribute, as well as sets out expectations for both contributors and edX engineering.

@singingwolfboy @jtauber can you take a look here and tell me what you think?

@carsongee would you mind also taking a look and letting me know what might be missing or is unclear from your perspective?

[singingwolfboy]

Mention one or two IRC resources here: webchat.freenode.net is particularly useful for people who just want to get on IRC as quickly as possible.

[sarina]

Can you give me some examples? I don't really know IRC well either... I just use a webclient that Julia invited me to.

[singingwolfboy]

IRCHelp is a good resource. For clients, the webchat is easiest, because you don't need to install anything and it's cross-platform. ChatZilla is almost as easy -- it's a Firefox extension, and works anywhere Firefox does. For an installed application, Pidgin works decently (or Adium on Mac), and has a familiar instant-messenger-style interface. For something truly dedicated to IRC, there's mIRC for Windows (free), LimeChat for Mac (free), or Textual for Mac (paid). There are also many other clients out there, but those are some good recommendations for people relatively new to IRC.

[singingwolfboy]

This is AWESOME, and super helpful! Thanks, @sarina!

[carsongee]

👍 This is a really nice step forward. It is much appreciated!

[sarina]

Thanks for the reviews, everybody!

I'm going to wait to merge this until James has a chance to review things (we may need to discuss the concept of open source community managers more fully).

[cahrens]

JavaScript coverage is included in the coverage report (and should also be 95% or greater).

[jrbl]

I think that this seems good.

[jtauber]

👍 from me

NOTE: Originally, the intention was that https://github.com/edx/edx-platform/wiki/How-To-Contribute would contain the contribution guidelines. I'd recommend either (1) copying your CONTRIBUTING.md content into the wiki page; (2) changing the wiki page to just link to CONTRIBUTING.md just so we don't have two documents that are out of sync.