Closes #6711: Add longtext custom field type with Markdown support

docs/models/extras/customfield.md

@@ -11,6 +11,7 @@ Within the database, custom fields are stored as JSON data directly alongside ea
 Custom fields may be created by navigating to Customization > Custom Fields. NetBox supports six types of custom field:
 
 * Text: Free-form text (up to 255 characters)
+* Long text: Free-form of any length; supports Markdown rendering
 * Integer: A whole number (positive or negative)
 * Boolean: True or false
 * Date: A date in ISO 8601 format (YYYY-MM-DD)

docs/release-notes/version-3.1.md

@@ -6,6 +6,7 @@
 ### Enhancements
 
 * [#1337](https://github.com/netbox-community/netbox/issues/1337) - Add WWN field to interfaces
+* [#6711](https://github.com/netbox-community/netbox/issues/6711) - Add `longtext` custom field type with Markdown support
 * [#6874](https://github.com/netbox-community/netbox/issues/6874) - Add tenant assignment for locations
 
 ### Other Changes