Update README.md

Added credits, feedback and license sections.

README.md

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-# data-model-patterns
+# Data Model Patterns
 A collection of data models that provide solutions to common problems in database design.
+
+## Credits
+
+The Conceptual Data Model models were prepared using the community edition of the  [ERwin](http://erwin.com/products/data-modeler/community-edition) Data Modeler.
+
+**Note:** The community edition of ERwin is limited to 25 model objects.
+
+## Feedback
+
+All bugs, feature requests, pull requests, feedback, etc., are welcome.
+
+## License
+
+This work is licensed under a [Creative Commons Attribution 4.0 International License] (http://creativecommons.org/licenses/by/4.0/).
+