Clarify the Codespaces requirements of the workshop in the README

[webchick]

This causes me anxiety. 😅

It'd be great for the instructions to clarify what the expected storage / core time requirements are for this workshop and some reassurance that it'll fit into the free plan (assuming that is, in fact, true. 😅 See above note about anxiety. 🤣 )

[webchick]

Ok, after WAY more horsing around than a typical attendee is going to do, here's where my usage is at.

Will make a PR that reflects this.