Update Config.zig

src/config/Config.zig

@@ -778,6 +778,9 @@ class: ?[:0]const u8 = null,
 ///
 ///   * only a single key input is allowed, `ctrl+a+b` is invalid.
 ///
+///   * for number modifier, write them out in letters instead of the actual
+///     number. Example: `ctrl+one` and _not_ `ctrl+1`.
+///
 ///   * the key input can be prefixed with `physical:` to specify a
 ///     physical key mapping rather than a logical one. A physical key
 ///     mapping responds to the hardware keycode and not the keycode