Update changelog

Author: rmk135

docs/main/changelog.rst

@@ -7,6 +7,11 @@ that were made in every particular version.
 From version 0.7.6 *Dependency Injector* framework strictly 
 follows `Semantic versioning`_
 
+Development version
+-------------------
+- Improve ``Dependency`` provider error message: when dependency is undefined,
+  error message contains its name.
+
 4.20.2
 ------
 - Move docs on container "self" injections to "Providers" section.