Hard to find spades features

[eliotmcintire]

In our future documentation, we need to make several things easier to find:

• [ ] continuing a simulation via end(sim) <- *later time*
• [x] caching
• [x] debugging (need a vignette/help file)
• many more ... fill in

[achubaty]

re: debugging, we have wiki entry that was linked in the module vignette.

I'll link from the intro vignette too and add the wiki link to the spades help.

[achubaty]

caching vignette was added a while ago