Add package orderers documentation

[BryceGattis]

Looking for some feedback on what exactly this page should look like. Some examples of the configuration are on the configuring rez page, but I'm not sure if we want the same kind of info here or not.

TODO:

• Not really sure what the purpose of the "per_family" orderer is. If each orderer can optionally specify what package families they affect, what is the point of an orderer whose purpose is exactly that?