Add a link to the user's guide

Author: Cito

README.md

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 DBUtils is a suite of tools providing solid, persistent and pooled connections to a database that can be used in all kinds of multi-threaded environments like Webware for Python or other web application servers. The suite supports DB-API 2 compliant database interfaces and the classic PyGreSQL interface.
 
 The current version supports Python Version 2.3 to 2.7.
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+See [Docs/UsersGuide.html](https://htmlpreview.github.io/?https://raw.githubusercontent.com/Cito/DBUtils/master/DBUtils/Docs/UsersGuide.html) for more explanation and usage information.
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