Create a doc that explains how to add FRB to an existing MonoGame project

[vchelaru]

Currently all docs are built around the idea that your game is already using FRB.

Have docs showing how to add FRB to a game.

[vchelaru]

Looks like there is already one, but it requires downloading .dlls and manually adding them to the project. Need to get the build (team city) working again, then get nugets for MonoGame 3.8.1 desktopgl