Document connection between `conditional_abunmatch` and `conditional_abunmatch_bin_based`

[aphearin]

The name change in #887 and #888 should be better explained so that users can understand the connection between the old and new algorithm.

It may also be worth mentioning the continued role of bin-based CAM together with the fuzzy_digitize function when using volume-limited galaxy samples that require different redshift selections as stellar mass is varied.