how to add deploy key for 2 repo with 1 user on github
You can create two public/private keys with whatever name you want:
~/.ssh repo1 repo1.pub repo2 repo2.pub config(Ie it doesn't have to be named id_rsa(.pub) to work, provided you indicate ssh where to look.
That is where 'config' comes into play: the config file includes the name of your two connections for GitHub repo1 and GitHub repo2 with, for each connection, the path to your private repo key, as described in "change github account mac command line" and in "Quick Tip: How to Work with GitHub and Multiple Accounts":
Host githubRepo1HostName github.comUser gitIdentityFile ~/.ssh/repo1Host githubRepo2HostName github.comUser gitIdentityFile ~/.ssh/repo2That way you can pull from any of the two repos, as long as you are using their ssh addresses.