better grid var comments

less/variables.less

@@ -349,6 +349,9 @@
 // Grid system
 // --------------------------------------------------
 
+// Number of columns in the grid system
 @grid-columns:              12;
+// Padding, to be divided by two and applied to the left and right of all columns
 @grid-gutter-width:         30px;
+// Point at which the navbar stops collapsing
 @grid-float-breakpoint:     768px;