Add release note

Author: mx-moth

docs/releases/development.rst

@@ -13,3 +13,4 @@ Next release (in development)
   Add :attr:`.Convention.time_coordinate` and :attr:`.Convention.depth_coordinate`,
   deprecate :meth:`.Convention.get_times()` and :meth:`.Convention.get_depths()`
   (:pr:`92`).
+* Add :meth:`.Convention.select_variables` (:pr:`93`).