Nuke Op Instructions Tweak

- Nuke Op Leaders get some additional instructions to help explain his role in the team.
- Newly spawned nukes will always have the code "ADMIN". All the game mode nukes already randomize a new code before they're used.
-  As a consequence of the above, the "tell the code" button in the Traitor Panel for ops will stop telling them the wrong code, because the game would sometimes give them the code to the station's nuke instead of their own