Updated openstack/openstack
Project: openstack/horizon  91023be1f1e417cc6aed1e35675c29ffedd05fbe
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Improve contributor documentation

Fix various errors in the contributor documentation:

- Factual mistakes (wrong file locations, etc)
- Formatting errors
- Typos

Change-Id: I4863ca10a532ac74491cfb19f8382e3d5287d2f3