Add note on what a Brawl is.

Session/HorsesBrawl.abc

@@ -3,6 +3,10 @@ T:Horse's Brawl
 T:Le Bransle des Chevaux
 R:Reel
 S:From Arbeau, Orchesographie, 1689
+N: Dottes: A _bransle_, or variously _branle_, _brawl_, _brall_,
+N:+ or _brantle_ is a type of simple renaissance French dance. The name
+N:+ comes from the verb _branler_ (to shake, wave, sway) and refers to
+N:+ the characteristic side-to-side movement of the dancers.
 O:France
 M:C|
 L:1/4