Add workaround for the descendant css combinator (space)

[CodeWithCory]

Currently spaces cannot be used in the action string CSS selectors in order to preserve the ease of a single-string action command. Recommend using >> instead. Should be able to replace >> with a space after the selector portion of the action string is already split off.

Note: >> is not a great solution because >> diverges from standard CSS, but I think it's worth it because it's relatively intuitive, will not conflict with existing CSS (because >> is invalid normally), and will unblock cases where using the descendant css combinator (space) would be helpful.

Example: click table>>.row:nth-child(2)>>button Edit Row // This would click an Edit button in the 2nd row of some table, regardless of how deeply nested. The resulting selector would be table .row:nth-child(2) button.

Also update the README so this functionality is well-documented.