vg setup improments

[JelteF]

• Figure out if .bashrc/.bash_profile/.profile should be changed
• Don't duplicate eval lines when running setup twice
• Don't edit files for shells that are not installed

[JelteF]

I've read stuff on the internet and it seems .bashrc is indeed the one that should be used. However, in that case the error message should that says vg eval is not eval-ed yet should be updated with hints for things to look at:

• Have you run vg setup?
• If so, your .bashrc is not sourced in this shell. Common reasons for this are:
  • You should add "the command" to ~/.bash_profile or ~/.profile instead
  • You're trying to run vg activate in a script. Either source ~/.bashrc or run "the command" in the script directly.

[JelteF]

Checklist of things:

• [x] Improve error message for not eval-ed yet
• [ ] Don't duplicate eval lines when running setup twice
• [ ] Don't edit files for shells that are not installed