Add suport for XDG Base Directory Specification

[alejandrosame]

Description

The install script asks for where to place the sync folder. However there's no prompt to confirm the location of the configuration file. It'd be a great addition for the script to adhere to the XDG base directory specification.

In that case, the configuration file could default to $XDG_CONFIG_HOME/SyftBox/config.json and the sync folder would default to $XDG_DATA_HOME/SyftBox.

Are you interested in working on this improvement yourself?

• Yes, I am. But I can't commit to it in the immediate future.

Additional Context

Add any other context or screenshots.