Allow custom systems

[XargonWan]

• Expose the custom_systems folder in retrodeck/ES-DE/custom_systems
• write a wiki article with some examples (like including the Steam library) and link the official ES-DE wiki article

[monkeyx-net]

I am currently using the custom system folder to get Ruffle to show and start

Am I missing how this is different?

[Daeymon]

I think they mean to symlink it from the .var location to the retrodeck folder. In the same way it has been done with the "collections" and "gamelist" folders. That way its contents is protected during updates.