How to include monogame reference in an existing project

I’m using monodevelop and want to switch a project from using XNA to Monogame. However when I go to Project > Edit References, I am unable to find MonoGame.Framework.Linux. It has definitely been installed because If I create a new Monogame Applicatino solution, it is there, but I don’t jnow how I would go about including it in an existing project?