improvement: Add Hint Option to all Widgets (#1429)

* Add hint to example admin config

* Add hint and hint position boolean above/below widget

* Style hint for both above and below widget

* Add hint and hint_above options to docs

* Remove hint above and make hint plaintext

website/content/docs/widgets/index.md

@@ -16,6 +16,7 @@ To see working examples of all of the built-in widgets, try making a 'Kitchen Si
 The following options are available on all fields:
 
 - `required`: specify as `false` to make a field optional; defaults to `true`
+- `hint`: optionally add helper text directly below a widget. Useful for including instructions.
 - `pattern`: add field validation by specifying a list with a [regex pattern](https://regexr.com/) and an error message; more extensive validation can be achieved with [custom widgets](https://www.netlifycms.org/docs/custom-widgets/#advanced-field-validation)
   - **Example:**
         ```yaml