docs(select): add section description to Rich Content Options

Author: brandyscarney

docs/api/select.md

@@ -203,7 +203,13 @@ import StartEndSlots from '@site/static/usage/v9/select/start-end-slots/index.md
 
 ## Rich Content Options
 
-TODO
+:::important
+Rich content in select options is disabled by default. Set [`innerHTMLTemplatesEnabled`](/docs/developing/config#ionicconfig) to `true` in your [global Ionic config](/docs/developing/config#global-config). Markup inside options is treated as plain text when it is disabled. Refer to [Security](/docs/techniques/security.md) for sanitization guidance when enabling custom HTML.
+:::
+
+In addition to single text labels, [Select Options](./select-option.md) can include HTML rich content in the select interface. Elements added inside of an option without a named slot will go into the default label. The `start` and `end` slots will place elements on either side of the default slot. The `description` attribute can be used for additional supporting text displayed under the label.
+
+This is separate from [Start and End Slots](#start-and-end-slots) on `ion-select`, which decorate the closed field. The rich content options display in the interface after opening the select.
 
 import RichContentOptions from '@site/static/usage/v9/select/rich-content-options/index.md';