Include description of reasonable machine requirements at the beginning of the tutorial

[huddlej]

Current Behavior

The tutorial provides no recommendations about what kind of hardware is required to run the workflows.

Possible solution

Include a brief description of what kind of hardware can be used (maybe distinguishing between running "locally" on a personal computer and on a cluster).

Additional context

This issue was originally raised by Stacia Wyman on the Nextstrain discussion board.