Add clarity around spell casting action / two spell casting

[aehernandez]

This could be added to the actions table: Essentially just this clarification:

A spell cast with a bonus action is especially swift. You must use a bonus action on your turn to cast the spell, provided that you haven't already taken a bonus action this turn. You can't cast another spell during the same turn, except for a cantrip with a casting time of I action.

https://www.dndbeyond.com/forums/dungeons-dragons-discussion/rules-game-mechanics/33821-quickened-spell-clarification