Clarify version policy for semver

Integrate additional topic that describes an high level overview
about semver v2, v3, and v3 and beyond.

README.rst

@@ -12,19 +12,8 @@ A Python module to simplify `semantic versioning`_.
 
 .. note::
 
-   This project works for Python 3.7 and greater only. If you are
-   looking for a compatible version for Python 2, use the
-   maintenance branch |MAINT|_.
-
-   The last version of semver which supports Python 2.7 to 3.5 will be
-   2.x.y However, keep in mind, the major 2 release is frozen: no new
-   features nor backports will be integrated.
-
-   We recommend to upgrade your workflow to Python 3 to gain support,
-   bugfixes, and new features.
-
-.. |MAINT| replace:: ``maint/v2``
-.. _MAINT: https://github.com/python-semver/python-semver/tree/maint/v2
+   This project works for Python 3.7 and greater only.
+   Refer to :ref:`version-policy` for more details.
 
 
 The module follows the ``MAJOR.MINOR.PATCH`` style:

changelog.d/pr431.doc.rst

@@ -0,0 +1,2 @@
+Clarify version policy for the different semver versions (v2, v3, >v3)
+and the supported Python versions.

docs/index.rst

@@ -16,6 +16,7 @@ Semver |version| -- Semantic Versioning
    migration/index
    advanced/index
    contribute/index
+   version-policy
    api
 
 .. toctree::

docs/version-policy.rst

@@ -0,0 +1,50 @@
+.. _version-policy:
+
+Version Policy
+==============
+
+.. |MAINT| replace:: ``maint/v2``
+.. _MAINT: https://github.com/python-semver/python-semver/tree/maint/v2
+.. |CHANGELOG| replace:: ``Changelog``
+.. _CHANGELOG: https://github.com/python-semver/python-semver/blob/maint/v2/CHANGELOG.rst
+
+The move from v2 to v3 introduced many changes and deprecated module functions.
+The main functionality is handled by the :class:`~semver.version.Version` class
+now. Find more information in the section :ref:`semver2-to-3`.
+
+
+semver Version 2
+----------------
+
+Active development of major version 2 has stopped. No new features nor
+backports will be integrated.
+We recommend to upgrade your workflow to Python 3 to gain support,
+bugfixes, and new features.
+
+If you still need this old version, use the  |MAINT|_ branch. There you
+can look for the |CHANGELOG|_ if you need some details about the history.
+
+
+semver Version 3
+----------------
+
+We will not intentionally make breaking changes in minor releases of V3.
+
+Methods marked as ``deprecated`` raise a warning message when used from the :py:mod:`warnings` module.
+Check section :ref:`sec_replace_deprecated_functions` to make your code
+ready for future major releases.
+
+
+semver Version 3 and beyond
+---------------------------
+
+Methods that were marked as deprecated will be very likely be removed.
+
+
+Support for Python versions
+---------------------------
+
+This project will drop support for a Python version when the
+following conditions are met:
+
+* The Python version has reached `EOL <https://devguide.python.org/versions/>`_.