Add doc for [cdkStickyRegion] and 'unstuckElement()'. Delete 'detach()' function, add its content into 'ngOnDestroy()'. 
Add doc for [cdkStickyRegion] and 'unstuckElement()'. Delete 'detach()' function, add its content into 'ngOnDestroy()'. 
sllethe/material2,sllethe/material2,sllethe/material2,sllethe/material2