Clarify pan/tilt/zoom settings (#245)

[eehakkin]

Split from #248 per @youennf's request.

[beaufortfrancois]

Following #248 (comment),

Web developers can already monitor the camera with PTZ permission with the permissions API to detect changes.

const panTiltZoomPermissionStatus = await navigator.permissions.query({
  name: "camera",
  panTiltZoom: true,
});

if (panTiltZoomPermissionStatus.state == "granted") {
  // User has granted access to this website to control camera PTZ.
}

panTiltZoomPermissionStatus.onchange = () => {
  // User has changed PTZ permission status.
}

[beaufortfrancois]

@youennf (gentle ping)

[youennf]

As I read it, this looks fine, though I would like to get some clarification to #250 (comment).

[beaufortfrancois]

@youennf Does it look good to you with recent changes around ideal PTZ constraints only in getUserMedia?

[youennf]

LGTM