Talk about alternate backends in documentation

[jamesdbrock]

https://discord.com/channels/864614189094928394/938253816862736405/961720347361701928

natefaubion —
One advantage of the new parsing implementation as well is that backends which support TCE can have a separate runner that has no trampoline. So for example, backends like erlang, lua, or scheme could get a performance boost without having to fork the library.