Add tornado extra options, update readme

Author: dhoomakethu

README.rst

@@ -104,6 +104,15 @@ permissions or a virtualenv currently running)::
     easy_install -U pymodbus
     pip install  -U pymodbus
 
+To Install pymodbus with twisted support run
+.. code-block:: python
+    pip install -U pymodbus[twisted]
+
+To Install pymodbus with tornado support run
+
+.. code-block:: python
+    pip install -U pymodbus[tornado]
+
 Otherwise you can pull the trunk source and install from there::
 
     git clone git://github.com/bashwork/pymodbus.git

setup.py

@@ -87,6 +87,9 @@
             'pyasn1 >= 0.1.4',
             'pycrypto >= 2.6'
         ],
+        'tornado': [
+            'tornado >= 4.5.3'
+        ]
     },
     test_suite='nose.collector',
     cmdclass=command_classes,