Add docs to an advanced section of createBound. [ci skip]

lodash.js

@@ -1589,21 +1589,28 @@
       var bindData = func && func.__bindData__;
       if (bindData && bindData !== true) {
         bindData = nativeSlice.call(bindData);
+
+        // set `thisBinding` is not previously bound
         if (isBind && !(bindData[1] & 1)) {
           bindData[4] = thisArg;
         }
+        // set if previously bound but not currently (subsequent curried functions)
         if (!isBind && bindData[1] & 1) {
           bitmask |= 8;
         }
+        // set curried arity if not yet set
         if (isCurry && !(bindData[1] & 4)) {
           bindData[5] = arity;
         }
+        // append partial left arguments
         if (isPartial) {
           push.apply(bindData[2] || (bindData[2] = []), partialArgs);
         }
+        // append partial right arguments
         if (isPartialRight) {
           push.apply(bindData[3] || (bindData[3] = []), partialRightArgs);
         }
+        // merge flags
         bindData[1] |= bitmask;
         return createBound.apply(null, bindData);
       }