update README with additional supported emulators (Ruffle, ...)

[skierpage]

README.md says

Currently works with three emulators: [MAME, EM-DOSBox, VICE]

but an Internet Archive blog article says

Utilizing an in-development Flash emulator called Ruffle, we have added Flash support to the Internet Archive’s Emularity system

and looking at loader.js, it also has a loader function for NP2, and possibly supports other mystery emulators xmil and vmac?