gitify - Setup both "origin" and "upstream" remotes

Note: This changes the call signature for "gitify", so we need to simultaneously update the wiki page.

Examples:

```bash
## Get code for Drupal. Use "https://github.com/civicrm" as "origin"
gitify Drupal /path/to/civicrm

## Get code for Drupal. Use "https://github.com/civicrm" as "upstream" and use "https://github.com/myuser" as origin. 
## And setup hooks.
gitify Drupal /path/to/civicrm --hooks --fork https://github.com/myuser

## Get code for Drupal. Use "git@github.com:civicrm" as "upstream" and use "git@github.com:myuser" as origin. 
## And setup hooks.
gitify Drupal /path/to/civicrm --hooks --fork git@github.com:myuser --upstream git@github.com:civicrm
```