change config location as per XDG Base Directory Specification

[yjqg6666]

Thanks for the awesome shellgpt. There might be some changes can be made.
According to the specification: https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html
Move config file to .config/shellgpt/config and move shellgpt to /usr/local/bin.

[kpatronas]

Good idea I will do this