Add support for GitHub EU

[richgo]

Expected this to succeed:
apm install https://somecompanyname.ghe.com/org-name/repo-name

Result:
'Only GitHub repositories are supported'
It is a GitHub repo, just enterprise managed users and not github.com

Fix:
Add to apm CLI

[richgo]

#8

[danielmeppiel]

I'm having a look at it this week. This should be supported.

[danielmeppiel]

Solved by #8

[danielmeppiel]

@richgo thank you for the PR, I have added documentation on how this works here https://github.com/danielmeppiel/apm/blob/main/docs/getting-started.md#github-enterprise-support

[richgo]

Thanks Daniel. Trying this out now 😀