home: create 'modules/home' folder

Consolidating all modules under the same path, to clear out the
top-level directory.

modules/home/secrets/secrets.nix

@@ -0,0 +1,9 @@
+# Common secrets
+let
+  keys = import ../../keys;
+
+  all = builtins.attrValues keys.users;
+in
+{
+  "github/token.age".publicKeys = all;
+}