gh-137533: document key type coercion limitations in json.loads

Doc/library/json.rst

@@ -364,6 +364,14 @@ Basic Usage
    .. versionchanged:: 3.9
       The keyword argument *encoding* has been removed.
 
+   .. note::
+
+      As mandated by RFC 8259, keys in JSON key-value pairs are always of
+      type :class:`str`. Therefore, dictionary keys obtained by
+      deserializing JSON objects will always be strings.
+      For Example,
+      ``json.loads('{"42":"value"}')`` returns the dictionary
+      ``{'42': 'value'}``.
 
 Encoders and Decoders
 ---------------------