Readd custom object documentation

Author: ftopic

fern/docs/pages/airdrop/initial-domain-mapping.mdx

@@ -115,6 +115,12 @@ Use the Chef UI to map record types and fields.
 The UI displays the external record types you defined in external domain metadata and allows you to map them to DevRev objects.
 Map one record type at a time, ensuring you map all required fields and as many optional fields as possible.
 
+#### Mapping as custom object
+The system allows importing record types and categories as custom objects. To achieve this you have to select `new_custom_object` when mapping the record type. For each external record type mapped as a custom object, a new custom **Leaf type** will be defined in DevRev and a **Subtype** will automatically be created. For more details on customization concepts, please refer to the
+[Customization](../customization.mdx) and [Custom Objects](../custom-objects.mdx)  documentation.
+
+The field mapping works the same as for the stock DevRev types, with the difference being that there are significantly fewer fields to map. All the unmapped fields of the external record type will be created as custom fields.
+
 ### Specify fallback mappings
 
 For some required DevRev fields a fallback is required.

fern/docs/pages/airdrop/metadata-extraction.mdx

@@ -561,6 +561,6 @@ be changed by the end user at any time, such as mandatory fields or custom field
   In the above example:
   - The external *type* field is declared as the `link_type_field`.
   - The `link_direction_names` provide a mapping of each value in the `link_type_field` to their directional names. `forward_name` and `backward_name` can be the same, but both are required.
-  - The human-readable name of the link type is taken from the enum values defined on the `link_type_field`. The linkable object types in DevRev will be defined based on the mappings of the *source_id* and *target_id* [fields](./supported-object-types.mdx#custom_link#).
+  - The human-readable name of the link type is taken from the enum values defined on the `link_type_field`. The linkable object types in DevRev are defined based on the mappings of the *source_id* and *target_id* [fields](./supported-object-types.mdx#custom_link#).
 
 </Steps>