Add container docs

docs/containers/reset_singletons.rst

@@ -18,6 +18,14 @@ Method ``.reset_singletons()`` also resets singletons in sub-containers: ``provi
    :lines: 3-
    :emphasize-lines: 21
 
+You can use ``.reset_singletons()`` method with a context manager. Singletons will be reset on
+both entering and exiting a context.
+
+.. literalinclude:: ../../examples/containers/reset_singletons_with.py
+   :language: python
+   :lines: 3-
+   :emphasize-lines: 14-15
+
 See also: :ref:`singleton-provider`.
 
 .. disqus::

examples/containers/reset_singletons_with.py

@@ -0,0 +1,23 @@
+"""Container reset singletons context manager example."""
+
+from dependency_injector import containers, providers
+
+
+class Container(containers.DeclarativeContainer):
+
+    service = providers.Singleton(object)
+
+
+if __name__ == '__main__':
+    container = Container()
+
+    service1 = container.service()
+
+    with container.reset_singletons():
+        service2 = container.service()
+
+    service3 = container.service()
+
+    assert service1 is not service2
+    assert service2 is not service3
+    assert service3 is not service1