Use Octotree with GitHub Enterprise

To use Octotree with GitHub Enterprise, add your GitHub Enterprise URL (say `https://github.ctb.com/`) to `GitHub Enterprise URLs`.

You need a personal access token for GitHub, so go to the following link (Replace `github.ctb.com` with your domain):

https://github.ctb.com/settings/tokens/new

and create one with the following option:

repo  Full control of private repositories

Provide the token to `Site access token`.

Reference:
https://github.com/buunguyen/octotree#access-token