[Arcs] "Holding" and "slots"

[jdyearsley]

Something needs to explain more clearly that when something can "hold" resources, golems, etc., it's equivalent to "has slots for".

[jdyearsley]

I decided to just add this as clarifications in the campaign FAQ. It's a little too niche to add errata for—I suspect it will cause more confusion than it clears up.