Add instructions to set up GitHub token

Signed-off-by: Shivam Sandbhor <shivam.sandbhor@gmail.com>

Author: sbs2001

README.rst

@@ -143,10 +143,32 @@ Tests
 Data import
 -----------
 
+Many data importers use GitHub APIs. For this, first set up value of the ``GH_TOKEN`` environment variable by running :
+
+::
+
+    export GH_TOKEN=yourgithubtoken
+
+
+See `GitHub docs  <https://docs.github.com/en/free-pro-team@latest/github/authenticating-to-github/creating-a-personal-access-token>`_ for instructions on how to obtain your GitHub token.
+
+
+To run all data importers use :
 ::
 
     DJANGO_DEV=1 python manage.py import --all
 
+To list available importers use :
+::
+
+    DJANGO_DEV=1 python manage.py import --list
+
+To run specific importers :
+::
+
+    DJANGO_DEV=1 python manage.py import rust npm 
+
+
 If you want to run the import periodically, you can use a systemd timer:
 
 ::
@@ -205,4 +227,4 @@ For full documentation about API endpoints.
 .. |Gitter chat| image:: https://badges.gitter.im/gitterHQ/gitter.png
    :target: https://gitter.im/aboutcode-org/vulnerablecode
 .. |PRs Welcome| image:: https://img.shields.io/badge/PRs-welcome-brightgreen.svg?style=flat-square
-   :target: http://makeapullrequest.com
+   :target: http://makeapullrequest.com