docs: clarify Quickstart POST example (#6960)

(fixes #6949)

---------

Co-authored-by: Nate Prewitt <nate.prewitt@gmail.com>

Author: E8Price

docs/user/quickstart.rst

@@ -271,7 +271,9 @@ use the same key::
       },
       ...
     }
-    >>> r1.text == r2.text
+    >>> # httpbin may embed non-deterministic metadata,
+    >>> # so we only compare our submitted data here.
+    >>> r1.json()['form'] == r2.json()['form']
     True
 
 There are times that you may want to send data that is not form-encoded. If