Dev_guide updated with github workflow

I tried to club the information scattered over the
internet,and made it suit to our need.These are the
resources i used:
1. https://help.github.com/articles/fork-a-repo
2. https://help.github.com/articles/using-pull-requests
3. https://help.github.com/articles/set-up-git
4. https://help.github.com/articles/checking-out-pull-requests-locally

Signed-off-by: Pushpesh Sharma <psharma@redhat.com>