Clarify how movement limits work

[ozkriff]

(from https://www.reddit.com/r/rust/comments/ale980/a_wasm_version_of_my_tactical_game)

It wasn't too obvious how the "move capacity" for each action was measured. For example, can you walk a certain number of squares or only a certain number of times?

Both conditions, actually. This needs to ba clarified in the UI and in the readme/guide.