add documentation for GitHub allauth configuration

related to #58

ippisite/docs/source/configuration.rst

@@ -51,6 +51,23 @@ You can then navigate to the django admin interface of iPPI-DB, and create an en
 .. image:: img/ORCID_conf_7.png
    :width: 100%
 
+GitHub authentication configuration
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The configuration for GitHub authentication follows the same principle: configure the app on the provider website, then enter the provided `Client ID` and `Client secret`
+on the django admin interface website.
+
+.. image:: img/Github_conf_1.png
+   :width: 100%
+
+.. image:: img/Github_conf_2.png
+   :width: 100%
+
+.. image:: img/Github_conf_3.png
+   :width: 100%
+
+
+
 Galaxy configuration
 --------------------