Clarify documentation: $INVENIO_WEB_INSTANCE

[tsgit]

related to user ticket:

https://rt.inspirehep.net/Ticket/Display.html?id=744421

I have a query regarding invenio-classifer. i am using ubuntu 16.04 lts. I installed the invenio-classifier using pip command.
but i am not able congiure ${INVENIO_WEB_INSTANCE}

can you help out to give step by step procedure to use this classifier.

I think the documentation could be improved in the README

https://github.com/inveniosoftware-contrib/invenio-classifier

also
https://github.com/inveniosoftware-contrib/invenio-classifier/search?utf8=%E2%9C%93&q=INVENIO_WEB_INSTANCE&type=

and here
https://pythonhosted.org/invenio-classifier/usage.html

It's not immediately obvious to third parties what is meant here.
T.