Add support for v language

[edam]

V (http://vlang.io) uses '.v' files.

[svercl]

Doesn't Verilog also use the .v extension?

[edam]

Yes, it does.

Also Coq (also supported by rg) uses .v files.

But if this is just about file selection, does it matter? Can't rg just support all three? 🤔