I tried to find info on this but, if it is documented, I was unable to find it. So I experimented.
One album had no information supplied by Roon so I devised a WORD file with graphics and text, converted it to pdf format, then saved the file in the MS Windows explorer music file. And hey presto - there it was ready to open in Roon.
So, if I do not like the ROON selected review of the album (and yes, that does apply to some) then I can add my own and add anything more I want about the album, even extending to opera Opera librettos!!! And these added files can be in a readable font size or can be expanded on the iPad to give a much more practical read than the small type offered in the booklets accompanying album sets.
ADDENDUM: Unfortunately what I describe above only works with music files I’ve downloaded. It appears that files from ripped CDs do not integrate with pdf files for display with Roon.
A task for developers?? @support