FFMpeg Check, Readme Update

Adds a screen during installation to inform the user about FFMpeg and asks if they have it installed, will automatically set "useffmpeg" to true or false depending on what they choose. Includes readme with more user friendly steps to set everything up.
are these nvm instructions no longer relevant, or should we move them back into the new block above where you instruct users to install nvm? I think the tool is dependent on node version >= 0.10.2