[Coco] building xroar

[Joel Rees]

Okay, I got it installed under ~/usr/bin , and it created xroar/roms
under ~/usr/share , but, of course, it doesn't know to look there.

I can, of course, specify that on the command line,

  xroar -m mc10 -bas ~/usr/share/xroar/roms/mc10.bin

works just fine, but it would be nice if there were a configuration to
have it look in a user-local install directory.

I'm sure there are more important things. Anyway, good work, and I'll
see if I can do something useful with this.