Add SESHion Manager (Ulauncher extension) to README

[mrinfinidy]

The original ulauncher extension (Sesh Session Manager) did not work on my system. That is why I forked it and added some new features:

• tmux doesn't have to be running
• open zoxide directories with tmux/sesh
• Selected tmux sessions will be focused if they are already open (in a window)
• If the session is not open SESHion-manager will open it in a new terminal window

I would really appreciate it if you could include my extension in your README.

[joshmedeski]

Thanks, it's nice seeing these improvements to the ulauncher experience!