Gentoo overlay repository seems to be missing some metadata
It seems the gentoo overlay is missing some metadata for "eselect repository" to work without specifying everything on command line:
eselect repository add tryton mercurial https://foss.heptapod.net/tryton/gentoo-overlay
I think the sync uri is missing in it or needs to be submitted somewhere. not sure about the exact procedure.
https://wiki.gentoo.org/wiki/Eselect/Repository
would be cool to have that fixed to not need to add it manually with the URL