Descripe the doc issue

In https://docs.opencv.org/4.x/d2/d53/classcv_1_1QuatEnum.html#abceb161bc29a481f2f55439ec723ee45
Matrices X(theta), Y(theta) Z(theta) are defined :

subscript is missing on the left side of equal (or subscript is useless on right side of equal)

Fix suggestion

PR
Add subscript on the left side of equal