Add docs and example

docs/providers/configuration.rst

@@ -306,6 +306,25 @@ configuration provider to strict mode.
 
    Modifier ``.required()`` should be specified before type modifier ``.as_*()``.
 
+Aliases
+-------
+
+You can use ``Configuration`` provider with a context manager to create aliases.
+
+.. literalinclude:: ../../examples/providers/configuration/configuration_alias.py
+   :language: python
+   :lines: 3-
+   :emphasize-lines: 14,22
+
+.. note::
+
+   Library ``environs`` is a 3rd party library. You need to install it
+   separately::
+
+      pip install environs
+
+   Documentation is available on GitHub: https://github.com/sloria/environs
+
 Injecting invariants
 --------------------
 

examples/providers/configuration/configuration_alias.py

@@ -0,0 +1,36 @@
+"""`Configuration` provider alias example."""
+
+from dependency_injector import containers, providers
+from environs import Env
+
+
+class Container(containers.DeclarativeContainer):
+
+    config = providers.Configuration()
+
+
+if __name__ == '__main__':
+    env = Env()
+    container = Container()
+
+    with container.config.some_plugin_name as plugin:
+        plugin.some_interval_ms.override(
+            env.int(
+                'SOME_INTERVAL_MS',
+                default=30000,
+            ),
+        )
+
+        with plugin.kafka as kafka:
+            kafka.bootstrap_servers.override(
+                env.list(
+                    'KAFKA_BOOTSTRAP_SERVERS',
+                    default=['kafka1', 'kafka2'],
+                ),
+            )
+            kafka.security_protocol.override(
+                env.str(
+                    'KAFKA_SECURITY_PROTOCOL',
+                    default='SASL_SSL',
+                ),
+            )