§5.1 in note add reference to ITU-T Series H supplement 1 for sign language requirements [RAUR]

[gunnarhm]

§5.1 Note gives references to sign language video quality requirements.
Add at the end of the note a document with research background and more details:
"and ITU-T Series H Supplement 1 "Sign language and lip-reading real-time conversation using low bit-rate video communication, https://www.itu.int/ITU-T/recommendations/rec.aspx?rec=4834&lang=en"

[RealJoshue108]

@gunnarhm good stuff, added to branch