git sync-fork

@kevgo I could use your help setting up tests as I'm unsure how to you want to go about this as would need to setup a fork. With a quick google search you can have remove repos on the same machine. Might be something worth trying. 

Here's a sample output:
```bash
$ git sync-fork
SYNCING THE CURRENT BRANCH WITH REMOTE UPSTREAM

Adder remote 'upstream' as https://github.com/Originate/end_state.git

Fetching updates for 'upstream'
From https://github.com/Originate/end_state
 * [new branch]      master     -> upstream/master

Merging 'upstream/master' into 'master'
Already up-to-date.

Pushing 'master' to Github
Everything up-to-date


*** ALL DONE ***

$ git sync-fork
SYNCING THE CURRENT BRANCH WITH REMOTE UPSTREAM

Fetching updates for 'upstream'

Merging 'upstream/master' into 'master'
Already up-to-date.

Pushing 'master' to Github
Everything up-to-date


*** ALL DONE ***

$ 
```
Can you please outline the basic use case for this new feature, ideally in the Readme file? I was under the impression that you just want to make it easy to sync existing forks. This also seems to create new upstream remotes for me. How would that work?