Update (almost) all the docs

docs/release_notes.rst

@@ -0,0 +1,23 @@
+.. _release_notes:
+
+Release notes
+=============
+
+Complete release notes can be found in the project's
+`GitHub releases page`_.
+
+Anymail practices `semantic versioning <semver>`_.
+Among other things, this means that minor updates
+(1.x to 1.y) should always be backwards-compatible,
+and breaking changes will always increment the
+major version number (1.x to 2.0).
+
+.. rubric:: PRE-1.0 DEVELOPMENT VERSIONS
+
+Anymail is under active, early development right now.
+Prior to a 1.0 alpha, features and APIs may change
+rapidly. (Per semver, the 0.x minor version will get
+bumped for any breaking changes before 1.0.)
+
+.. _GitHub releases page: https://github.com/anymail/django-anymail/releases
+.. _semver: http://semver.org