DOC: release notes

RELEASE.rst

@@ -10,10 +10,18 @@ pandas 0.5.0
 
 **Release date:** not yet released
 
-
-
-Thanks to Thomas Kluyver and others for contributing patches and feedback
-leading to some of the minor API changes listed below.
+This major release of pandas includes a number of API changes (see below) and
+cleanup of deprecated APIs from pre-0.4.0 releases. There are also bug fixes,
+some new features, performance enhancements, and includes a new IPython
+completer hook to enable tab completion of DataFrame columns accesses as
+attributes (a new feature).
+
+In addition to the changes listed here from 0.4.3 to 0.5.0, the minor releases
+0.4.1, 0.4.2, and 0.4.3 brought some significant new functionality and
+performance improvements that are worth taking a look at.
+
+Thanks to Thomas Kluyver and others for contributing patches and providing
+feedback on the library.
 
 **API Changes**