Updated README with overview and guidance on forking, translations, and development

[brockfanning]

I submitted a pull-request with an updated README, but figured I'd start an issue here for easier feedback. You can see the updated guide here.

This is intended to be an update and expansion of the Quick Start guide. Feedback welcome!

[JenPark9]

Thank you, Brock. I am asking Angela and Phil to review. I will review as well.

[JenPark9]

Kali, please follow up with Phil and Angela on this to get their feedback. Thank you!

[angela-smithers]

Hello,
For the link to "Install GitHub software", are you trying to go here: https://git-scm.com?

When I clicked the hyperlink, it told me the page does not exist. It sent me here: https://help.github.com/desktop/guides/getting-started/installing-github-desktop/#platform-mac

[angela-smithers]

This line may be redundant:

Just one or the other

[brockfanning]

@SmithersA Thanks, I'll make a PR to fix those.

[brockfanning]

@SmithersA @philipashlock I created wiki pages for each of the sections of the README, and submitted a PR for your consideration, to prune the README and point to the wiki instead: #862
Angela, I fixed those issues you found in the new wiki pages. Thanks for catching those!