Shibboleth administration guide

This is a draft article for explaining a basic shibboleth identity provider install and configuration.

**edit**: [Rendered](https://github.com/jch/saml/blob/shibboleth-administration/shibboleth-administration.md)

cc @michaeltwofish @mtodd @sbryant @lildude
We should state the path and filename to indicate this is the attribute-filter.xml file.