(ios) add PreferredContentMode preference documentation (#1083)
(ios) add PreferredContentMode preference documentation (#1083)

* (ios) add PreferredContentMode preference

* Update index.md

* Update www/docs/en/dev/config_ref/index.md
apache/cordova-docs,apache/cordova-docs,apache/cordova-docs,apache/cordova-docs,purplecabbage/cordova-docs,purplecabbage/cordova-docs,purplecabbage/cordova-docs,purplecabbage/cordova-docs