Add some way for players to tell how they could buy an upgrade sooner

[knexer]

That is, what resource are they having to save up the longest in order to buy the thing? What resource are they unable to get enough of even by the end of time?

Could be an on-hover update to the resource panel.
Could be part of the buy upgrade button.
Could be part of the cost description for the upgrade.

It'd also be nice to see this info for upgrades in other timelines, or in the past of this one. In that case it'd either have to be an on-hover resource panel update or part of the upgrade indicator tooltip. It could perhaps say something like 'had enough metal 2 cycles ago' or 'had enough volatiles this cycle'.