add note about single vs group

Author: mdo

docs/4.0/components/buttons.md

@@ -116,7 +116,7 @@ Add `data-toggle="button"` to toggle a button's `active` state. If you're pre-to
 
 ### Checkbox and radio buttons
 
-Bootstrap's `.button` styles can be applied to other elements, such as `<label>`s, to provide checkbox or radio style button toggling. Add `data-toggle="buttons"` to a `.btn-group` containing those modified buttons to enable their toggling behavior via JavaScript and add `.btn-group-toggle` to style the `<input>`s within your buttons.
+Bootstrap's `.button` styles can be applied to other elements, such as `<label>`s, to provide checkbox or radio style button toggling. Add `data-toggle="buttons"` to a `.btn-group` containing those modified buttons to enable their toggling behavior via JavaScript and add `.btn-group-toggle` to style the `<input>`s within your buttons. **Note that you can create single input-powered buttons or groups of them.**
 
 The checked state for these buttons is **only updated via `click` event** on the button. If you use another method to update the input—e.g., with `<input type="reset">` or by manually applying the input's `checked` property—you'll need to toggle `.active` on the `<label>` manually.