Add note for HiddenField behavior (#9055)

* Add note for HiddenField behavior

* Update docs/api-guide/fields.md

* Update docs/api-guide/validators.md

---------

Co-authored-by: Asif Saif Uddin <auvipy@gmail.com>

Author: denisSurkov

docs/api-guide/fields.md

@@ -558,6 +558,12 @@ The `HiddenField` class is usually only needed if you have some validation that
 
 For further examples on `HiddenField` see the [validators](validators.md) documentation.
 
+---
+
+**Note:** `HiddenField()` does not appear in `partial=True` serializer (when making `PATCH` request). This behavior might change in future, follow updates on [github discussion](https://github.com/encode/django-rest-framework/discussions/8259). 
+
+---
+
 ## ModelField
 
 A generic field that can be tied to any arbitrary model field. The `ModelField` class delegates the task of serialization/deserialization to its associated model field.  This field can be used to create serializer fields for custom model fields, without having to create a new custom serializer field.

docs/api-guide/validators.md

@@ -164,6 +164,12 @@ If you want the date field to be entirely hidden from the user, then use `Hidden
 
 ---
 
+---
+
+**Note:** `HiddenField()` does not appear in `partial=True` serializer (when making `PATCH` request). This behavior might change in future, follow updates on [github discussion](https://github.com/encode/django-rest-framework/discussions/8259). 
+
+---
+
 # Advanced field defaults
 
 Validators that are applied across multiple fields in the serializer can sometimes require a field input that should not be provided by the API client, but that *is* available as input to the validator.