Clarify custom spatial granularity support

spatial_serving/examples/probability_npz_contract.json

@@ -17,6 +17,6 @@
   },
   "notes": [
     "The names can be overridden with CLI flags.",
-    "The released FireWx-FM checkpoint is native-grid first; county and sub-county outputs are serving aggregations."
+    "The released FireWx-FM checkpoint is native-grid first; county, sub-county, and other custom polygon granularities are serving aggregations."
   ]
 }