maintainers/team-list: Set GitHub team for docs team

Makes it so that the docs team gets pinged for each release

maintainers/team-list.nix

···
 
   docs = {
     members = [ ];
+    githubTeams = [
+      "documentation-team"
+    ];
     scope = "Maintain nixpkgs/NixOS documentation and tools for building it.";
     shortName = "Docs";
     enableFeatureFreezePing = true;