youtube.lua: document an "n" descrambling transformation

share/lua/playlist/youtube.lua

@@ -286,6 +286,7 @@ function n_descramble( nparam, js )
         alphabet2 = {
             func = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_",
             match = {
+                -- function(){for(var d=64,e=[];++d-e.length-32;){switch(d){case 58:d-=14;case 91:case 92:case 93:continue;case 123:d=47;case 94:case 95:case 96:continue;case 46:d=95}e.push(String.fromCharCode(d))}return e}
                 -- function(){for(var d=64,e=[];++d-e.length-32;)switch(d){case 46:d=95;default:e.push(String.fromCharCode(d));case 94:case 95:case 96:break;case 123:d-=76;case 92:case 93:continue;case 58:d=44;case 91:}return e}
                 "^function%(%){[^}]-case 58:d%-=14;",
                 "^function%(%){[^}]-case 58:d=44;",