Clarifiyng documentation for parameterize

- Added snippet dealing with parameterize run order of tests

doc/en/parametrize.rst

@@ -126,6 +126,22 @@ To get all combinations of multiple parametrized arguments you can stack
 This will run the test with the arguments set to ``x=0/y=2``, ``x=0/y=3``, ``x=1/y=2`` and
 ``x=1/y=3``.
 
+Due to how decorators work it runs in reverse of expected order.
+In this case::
+
+    $ pytest
+    =========================== test session starts ============================
+    platform linux -- Python 3.x.y, pytest-3.x.y, py-1.x.y, pluggy-0.x.y
+    rootdir: $REGENDOC_TMPDIR, inifile:
+    collected 4 items
+
+    test.py::test_foo[2-0] PASSED                                        [ 25%]
+    test.py::test_foo[2-1] PASSED                                        [ 50%]
+    test.py::test_foo[3-0] PASSED                                        [ 75%]
+    test.py::test_foo[3-1] PASSED                                        [100%]
+
+    ========================== 4 passed in 0.01 seconds ========================
+
 .. _`pytest_generate_tests`:
 
 Basic ``pytest_generate_tests`` example