versioning: add fulcrum db change info

Author: erikarvstedt

examples/configuration.nix

@@ -292,5 +292,5 @@
   # The nix-bitcoin release version that your config is compatible with.
   # When upgrading to a backwards-incompatible release, nix-bitcoin will display an
   # an error and provide instructions for migrating your config to the new release.
-  nix-bitcoin.configVersion = "0.0.70";
+  nix-bitcoin.configVersion = "0.0.85";
 }

modules/versioning.nix

@@ -231,6 +231,15 @@ let
         The `lndconnect-rest-onion` binary has been renamed to `lndconnect-onion`.
       '';
     }
+    {
+      version = "0.0.85";
+      condition = config.services.fulcrum.enable;
+      message = ''
+        Fulcrum 1.9.0 has changed its database format.
+        The database update happens automatically and instantly on deployment,
+        but you can't switch back to an older Fulcrum version afterwards.
+      '';
+    }
   ];
 
   mkOnionServiceChange = service: {