Add installation guides

This starts two guides, one aimed at general users and one aimed at developers. The only entry in both guides is instructions for installation. The user installation guide is simple as all major distributions include the necessary packages. The developer guide is more in-depth and is largely made up of pointers to other project's documentation.

However, the out-of-tree module includes no documentation so that is included here. It could be moved to a README in the repository if folks wish, though.