docs: add changelog update for //python/bin (bazel-contrib#2616)

This was a forgotten part of the original PR (bazel-contrib#2507) implementing it.

Author: rickeylev

CHANGELOG.md

@@ -60,7 +60,9 @@ Unreleased changes template.
 
 {#v0-0-0-added}
 ### Added
-* Nothing added.
+* {obj}`//python/bin:python`: convenience target for directly running an
+  interpreter. {obj}`--//python/bin:python_src` can be used to specify a
+  binary whose interpreter to use.
 
 {#v0-0-0-removed}
 ### Removed