Better documentation of each CRD and it's options

Some CRDs for this operator, especially the [SolrCloud CRD](https://github.com/bloomberg/solr-operator/blob/master/config/crd/bases/solr.bloomberg.com_solrclouds.yaml), are getting extrememly large. This is because we are importing options from base kubernetes objects, which expand out to be extremely large.

Because these files are much too big to parse, we should have documentation for each CRD, explaining at least the basics of using each one. Eventually we can hopefully start to use links to the other types of resources, so they don't have to be explicitly listed in our CRDs. But for now I think the solution is just to add better documentation.

Start with config/crd/bases/solr.bloomberg.com_solrclouds.yaml and identify the operator's other CRD definitions. Determine where documentation for each CRD should live and which basic options users need; done means every CRD has accessible documentation without requiring readers to parse the oversized generated schemas.

Written by the indexing model from the issue text.