Confirm officials signing keys correlation to core developer

[szpak]

In respect to #984 it would be good to confirm that mentioned signing keys are provided by the Spock core developer(s).

It could be done for example by adding/modifying them in a commit signed itself by the private key of the core developer which in turn is associated to him (or his public acocunts) using https://keybase.io/ or some f2f meeting.