Add better support for github.com Personal Access Tokens PAT

there is no clear way to add an account via personal access token for a github.com account

Steps to reproduce:

1. Tools -> Options -> Authentication -> Add
2. select  "GitHub" as the hosting service.
3. Look at list of Authentication options

Currently the selectable Authentication options are "Basic" and "OAuth".

Desired solution: add: "personal access token" as a third selectable authentication option.

Other git software, such as git fork, has this option.

Workaround solution 1: At the very least there should be an official help article by Atlassian with step by step instructions on how to add an a GitHub personal access token account to Source Tree.  Currently multiple people are posting different ways / workarounds in forums and they either don't work or are hard to follow.