Possibly incorrect note on focusMode

[JohnHardy]

In "10. Photo Capabilities and Constrainable Properties" point 3 it says "Focus mode describes the focus setting of the capture device (e.g. auto or manual)."

However, focusMode is defined as "A sequence of supported focus modes. Each string MUST be one of the members of MeteringMode." Of which the values none, manual, single-shot, or continuous

To fix this issue, we could instead link to the MeteringMode enum.