Feature Request: Supported shells are printed whenever `Error: shell * is still not supported` is printed

[magnus-ISU]

Even looking at the code, maybe its because I don't know Go really well but I can't figure out what is supported :P

It seems to me like the supported shells should be known at compile time. However, it is a map which shells are added to at runtime which confuses me.

I would like to try to add ion support, but am confused by what is going on.

[doron-cohen]

This was an overkill design choice looking back. I think I should just hold all shells in one global list. Next time I will get to that part in the code I will refactor.