db sqlalchemy migration README update

[Kanagaraj Manickam]

sqlalchemy is now being managed by openstack and README is still holding the url to the google repo. This bug is filed to update the repo reference to https://github.com/stackforge/sqlalchemy-migrate

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/169680

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/169680
Committed: https://git.openstack.org/cgit/openstack/heat/commit/?id=35f964cae4adbdd8a7047186122034b3395f7111
Submitter: Jenkins
Branch: master

commit 35f964cae4adbdd8a7047186122034b3395f7111
Author: Kanagaraj Manickam <email address hidden>
Date: Wed Apr 1 12:29:13 2015 +0530

    Updates migrate_repo README

    sqlalchemy migrate utility is being maintained by
    Openstack Stackforge project, which was maintained
    by google earlier. So the README is updated with
    Stackforge project url.

    Change-Id: I824d2ede84da8dd8a1488c0ca5e3ee0a71fb7810
    Closes-bug: #1439023