Update documentation to include --pythonpath to set up the example app (#1270)

Add --pythonpath to instructions for setting up example app

Author: Vitalii-Kh95

README.rst

@@ -149,9 +149,9 @@ installed and activated:
     $ git clone https://github.com/django-json-api/django-rest-framework-json-api.git
     $ cd django-rest-framework-json-api
     $ pip install -Ur requirements.txt
-    $ django-admin migrate --settings=example.settings
-    $ django-admin loaddata drf_example --settings=example.settings
-    $ django-admin runserver --settings=example.settings
+    $ django-admin migrate --settings=example.settings --pythonpath .
+    $ django-admin loaddata drf_example --settings=example.settings --pythonpath .
+    $ django-admin runserver --settings=example.settings --pythonpath .
 
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