Restructure topics on phone connections
Provide a summary of how to connect phones to the computer, focus on net tethering.
Reuse stub pages:
- https://gitlab.gnome.org/GNOME/gnome-user-docs/blob/master/gnome-help/C/hardware-phone-connecting.page.stub
- https://gitlab.gnome.org/GNOME/gnome-user-docs/blob/master/gnome-help/C/net-tethering.page.stub
Reference https://gitlab.gnome.org/GNOME/gnome-user-docs/blob/master/gnome-help/C/net-mobile.page.