Git Guide: expand on creating a Github account

[digitaldrummerj]

Feedback that I received on the forking section:

Step 0 for forking the repository is "login to Github and/or create a Github account". We might want to mention that they may want to separate their personal, open-source contributions from their profession, employer-sponsored accounts.

Might also want to clarify the difference between github.com and Github enterprise since more and more people have Github enterprise accounts but not github.com accounts.

[AbisoyeAlli]

I can take this one