Add note that scripted fields will reject documents with a source value in their field (#71340)

docs/reference/mapping/types/numeric.asciidoc

@@ -156,7 +156,9 @@ The following parameters are accepted by numeric types:
 
     If this parameter is set, then the field will index values generated
     by this script, rather than reading the values directly from the
-    source. Scripts are in the same format as their
+    source. If a value is set for this field on the input document, then
+    the document will be rejected with an error.
+    Scripts are in the same format as their
     <<runtime-mapping-fields,runtime equivalent>>. Scripts can only be
     configured on `long` and `double` field types.