add comment on sample configuration

deployment/options.nix

@@ -8,6 +8,8 @@
   This can be fixed if we made the converter aware of [`$defs`], but that would likely amount to half a rewrite.
 
   [`$defs`]: https://json-schema.org/understanding-json-schema/structuring#defs
+
+  An example deployment configuration may be found at `configuration.sample.json`.
 */
 {
   lib,