Update the README's discussion of early exits

[unforgettableid]

The README stated that ⎄ Compose q led to an early exit. As @MaaaxiKing has pointed out, this statement is now outdated. The statement is no longer correct.

In truth, ⎄ Compose q no longer leads to an early exit. But ⎄ Compose Q still does.

This commit updates the README to use a capital Q instead of a lowercase q.