respect XDG Base Directory Specification on Linux and document handling on Windows/OSX

[goern]

The 'XDG Base Directory Specification' should be respected on GNU/Linux systems, as crc should not assume that it is ok to use $HOME/.crc

Handling of XDG ENV vars on other operating systems should be documented. At least most of the ENV should be respected on OSX.

[praveenkumar]

@goern we did think of it and since minishift/minikube also use $HOME/.<project> we went through this route instead of XDG Base Directory Specification so a user coming from these project should know where to look for files, in future, we should consider this.

[cfergeau]

In my opinion, once we have our initial releases, this will be much harder to change, so this really should be done early.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.