As of now, if you right-click networkmanager, edit connections, and hit the plus, you can manually create a wireguard profile as the link instructs. However, you cannot import a wireguard profile via the gui yet.
If you use nmcli it will work. See the link, then scroll down to the first comment, by Eugene, and you can import the wireguard profile. Be warned, however, that even if you import with nmcli, features such as the killswitch are not yet respected by networkmanager If the VPN fails, data WILL be passed in clear.
Hopefully in the future, the networkmanager team will have a rock-solid feature where wireguard profiles can be imported via the gui and perform as expected, killswitches, multihop, and all. Maybe even they can add a feature where a random profile is selected on startup, given that wireguard has no remote-random feature like openvpn.