Added some notes to the README.

README.txt

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+This is a fork of https://launchpad.net/django-openid-auth. It has the following differences from upstream:
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+* https://github.com/edx/django-openid-auth/pull/1.
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+To bring in the latest changes:
+1. Import commits from the bazaar repo to the `upstream` branch of this repo using https://design.canonical.com/2015/01/converting-projects-between-git-and-bazaar/.
+2. Merge them into master.
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+
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 = Django OpenID Authentication Support =
 
 This package provides integration between Django's authentication