Add disqus comments for introduction documents

docs/introduction/di_in_python.rst

@@ -129,3 +129,6 @@ using :doc:`Dependency Injector <../index>`:
 .. literalinclude:: ../../examples/miniapps/engines_cars/example_ioc_containers.py
    :language: python
    :linenos:
+
+
+.. disqus::

docs/introduction/key_features.rst

@@ -43,3 +43,6 @@ Components of *Dependency Injector* framework could be used:
 
 Main idea of *Dependency Injector* framework is to be useful tool for the 
 right thing.
+
+
+.. disqus::

docs/introduction/structure.rst

@@ -45,3 +45,6 @@ Containers could be:
 + Overridden by each other.
 + Copied from each other.
 + Extended.
+
+
+.. disqus::

docs/introduction/what_is_di.rst

@@ -116,6 +116,9 @@ And `John Munsch`_ provided absolutely Great answer:
     down to eat.
 
 
+.. disqus::
+
+
 .. _Dependency injection: http://en.wikipedia.org/wiki/Dependency_injection
 .. _Inversion of control: https://en.wikipedia.org/wiki/Inversion_of_control
 .. _Dependency inversion: https://en.wikipedia.org/wiki/Dependency_inversion_principle