Add page for LDAP documentation

<a href="https://github.com/jooola"><img src="https://avatars2.githubusercontent.com/u/19195485?v=3" align="left" width="96" height="96" hspace="10"></img></a> **Issue by [jooola](https://github.com/jooola)**
_Saturday May 27, 2017 at 04:21 GMT_
_Originally opened as https://github.com/Libresonic/documentation/issues/8_

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