docs(item): improve documentation behind item
docs(item): improve documentation behind item

adds more usage examples and content projection information.

closes driftyco/ionic-site#579
references #5993

AbraaoAlves/ionic,joshesp/ionic,dennybiasiolli/ionic,joshesp/ionic,alan-agius4/ionic,jhlee8804/ionic,joshesp/ionic,TillaTheHun0/ionic,jhlee8804/ionic,TillaTheHun0/ionic,manucorporat/ionic,AbraaoAlves/ionic,manucorporat/ionic,jarrodkoch/ionic,driftyco/ionic,TillaTheHun0/ionic,jhlee8804/ionic,dennybiasiolli/ionic,jarrodkoch/ionic,jarrodkoch/ionic,brianespinosa/ionic2-sass,alan-agius4/ionic,janglednerves/ionic,dennybiasiolli/ionic,dennybiasiolli/ionic,manucorporat/ionic,driftyco/ionic,joshesp/ionic,AbraaoAlves/ionic,jarrodkoch/ionic,driftyco/ionic,manucorporat/ionic,manucorporat/ionic,janglednerves/ionic,alan-agius4/ionic,driftyco/ionic,cambronjay/ionic,cambronjay/ionic,janglednerves/ionic,janglednerves/ionic,AbraaoAlves/ionic,cambronjay/ionic,dennybiasiolli/ionic,alan-agius4/ionic,TillaTheHun0/ionic,jhlee8804/ionic,driftyco/ionic,jarrodkoch/ionic,AbraaoAlves/ionic,alan-agius4/ionic,cambronjay/ionic,alan-agius4/ionic,janglednerves/ionic,cambronjay/ionic,jhlee8804/ionic