Adds snippet showing transcription of mensural music to modern

I've now taken the snippet I added to the LSR concerning using the same underlying music to create both mensural and modern music, and added it to the NR where previously there was a ToDo.  It's probably not perfect, but seems an improvement to me.

Please ignore the headword snippets: this seems a feature of LSR import and the final push doesn't normally show them.

[PhilEHolmes, 2015-05-20 10:09:13]

Please review.