Update using.rst

Additional informations about installing on Centos 7

docs/using.rst

@@ -64,6 +64,11 @@ Mac OSX
 
    sudo ./bootstrap/mac.sh
 
+Centos 7
+--------
+.. code-block:: shell
+
+   sudo ./bootstrap/centos.sh
 
 Installation
 ============
@@ -73,6 +78,13 @@ Installation
    virtualenv --no-site-packages -p python2 venv
    ./venv/bin/pip install -r requirements.txt
 
+Installation on Centos 7
+============
+
+.. code-block:: shell
+
+   virtualenv --no-site-packages -p python2 venv
+   env SWIG_FEATURES="-cpperraswarn -includeall -D__`uname -m`__ -I/usr/include/openssl" ./venv/bin/python setup.py install
 
 Usage
 =====