Editorial comments on requirements document

A tiny nit in the Introduction section. The link to the DAP charter is
pointing to the old charter. The correct one should be
http://www.w3.org/2011/07/DeviceAPICharter, where the relevant deliverable
is
*	Capture API, an API to manage a device's camera and microphone, e.g.
to take a picture or record a sound

- Cathy.