Add docs

docs/usage.md

@@ -92,6 +92,16 @@ and more. These areas allow you to view, add, edit, delete and manage permission
 for these objects. You can also manage saved views, mail accounts, mail rules,
 workflows and more from the management sections.
 
+### Nested Tags
+
+Paperless-ngx v2.19 introduces support for nested tags, allowing you to create a
+hierarchy of tags, which may be useful for organizing your documents. Tags can
+have a 'parent' tag, creating a tree-like structure, to a maximum depth of 5. When
+a tag is added to a document, all of its parent tags are also added automatically
+and similarly, when a tag is removed from a document, all of its child tags are
+also removed. Additionally, assigning a parent to an existing tag will automatically
+update all documents that have this tag assigned, adding the parent tag as well.
+
 ## Adding documents to Paperless-ngx
 
 Once you've got Paperless setup, you need to start feeding documents