Remove inter-row references in README table

[MattBrauer]

In the README file the table describing the lists has a couple of rows for which the description and references include something like "union of previous lists" or "see previous lists". This makes it hard to reliably extract list metadata: the order of the lists in the table is presumably not guaranteed, and this indirection is not really necessary anyway.

I'd suggest making sure that each row is self-sufficient, with explicit descriptions (e.g., "union of gpcr_guide and gpcr_uniprot") and complete references, even if this risks duplicating information. That way when a list's metadata is extracted from its table row, there will be no need to refer to other rows in order to get the complete information.