Clarify upload modal copy.
Clarify upload modal copy.

https://unisubs.sifterapp.com/issue/1152
pculture/unisubs,wevoice/wesub,norayr/unisubs,pculture/unisubs,ujdhesa/unisubs,pculture/unisubs,eloquence/unisubs,ReachingOut/unisubs,ReachingOut/unisubs,wevoice/wesub,ujdhesa/unisubs,norayr/unisubs,wevoice/wesub,eloquence/unisubs,ofer43211/unisubs,ujdhesa/unisubs,ujdhesa/unisubs,ReachingOut/unisubs,eloquence/unisubs,norayr/unisubs,norayr/unisubs,pculture/unisubs,ofer43211/unisubs,ReachingOut/unisubs,wevoice/wesub,eloquence/unisubs,ofer43211/unisubs,ofer43211/unisubs