i#3856: Add VSIB operand creation documentation (#3857)
i#3856: Add VSIB operand creation documentation (#3857)

Adds a note to opnd_create_disp() that it is the document method for creating a VSIB memory reference operand.

Fixes #3856 

AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio