Clarified docs for Python 2 and added limitations

Details:

* Docs: In the Introduction section, removed statements about the nocasedict
  behavior in Python 2.

* Docs: In the Introduction section, documented the limitation that 'd | other'
  and 'd |= other' which were added to the standard Pyton 'dict' class in Python
  3.9 are not yet supported by nocasedict.

Signed-off-by: Andreas Maier <[email protected]>

docs/changes.rst

@@ -69,14 +69,21 @@ Released: not yet
   dependencies, and added a step to the test workflow that runs it.
   (issue #176)
 
+* Docs: In the Introduction section, documented the limitation that 'd | other'
+  and 'd |= other' which were added to the standard Pyton 'dict' class in Python
+  3.9 are not yet supported by nocasedict.
+
 **Cleanup:**
 
 * Dev: Removed description of stable branches in development.rst because this
   project maintains only the master branch. (issue #171)
 
-* Converted percent-style and format() basedd string formatting to f-strings.
+* Converted percent-style and format() based string formatting to f-strings.
   (issue #174)
 
+* Docs: In the Introduction section, removed statements about the nocasedict
+  behavior in Python 2.
+
 **Known issues:**
 
 * See `list of open issues`_.

docs/intro.rst

@@ -29,15 +29,13 @@ Example:
     NocaseDict({'Alpha': 1, 'Beta': 2})
 
 The :class:`~nocasedict.NocaseDict` class supports the functionality of the
-built-in `dict class of Python 3.8`_ on all Python versions it supports with
-the following exceptions (and the case-insensitivity of course):
+built-in `dict class of Python 3.8`_ on all Python versions it supports.
 
-* The ``iter..()``, ``view..()`` and ``has_key()`` methods are only present
-  on Python 2, consistent with the built-in ``dict`` class.
+Limitation: Any functionalities added to the ``dict`` class in Python 3.9 or
+later are not yet supported. These are:
 
-* The ``keys()``, ``values()`` and ``items()`` methods return a list on Python 2
-  and a dictionary view on Python 3, consistent with the built-in ``dict``
-  class.
+* ``d | other`` - Added in Python 3.9.
+* ``d |= other`` - Added in Python 3.9.
 
 .. _dict class of Python 3.8: https://docs.python.org/3.8/library/stdtypes.html#dict