Mapping rec2100-pq to [0,1] underdefined

[svgeesus]

From rec2100-pq

NOTE: {R', G', B'} are in the range [0, 1], i.e. they are not expressed in cd/m2

Suggest to add:

The R'G'B' value 1,1,1 corresponds to a luminance of 10,000 cd/m^2