Improve installation docs

A discussion at http://www.mqseries.net/phpBB2/viewtopic.php?p=300208 highlighted the need for a better approach towards installation guide. Instead of assuming that PyMQI users are always Python programmers familiar with all the (very simple, but still) Python build tools, there should be rather created some sort of step by step guides for installing PyMQI under Windows and Linux, using either pip/PyPI or Python's standard setuptools.