website/docs: add group hierarchy docs

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

website/docs/user-group/group.md

@@ -0,0 +1,13 @@
+---
+title: Group
+---
+
+## Hierarchy
+
+Groups can be children of another group. Members of children groups are effective members of the parent group.
+
+When you bind a group to an application or flow, any members of any child group of the selected group will have access.
+
+## Attributes
+
+Attributes of groups are recursively merged, for all groups the user is a *direct* member of.

website/docs/user-group/user.md

@@ -26,10 +26,11 @@ See [Troubleshooting access problems](../troubleshooting/access.md), when set, t
 This field is only used by the Proxy Provider.
 :::
 
-Some applications can be configured to create new users using header information forwarded from Authentik. You can forward additional header information by adding each header 
+Some applications can be configured to create new users using header information forwarded from Authentik. You can forward additional header information by adding each header
 underneath `additionalHeaders`:
 
 #### Example:
+
 ```
 additionalHeaders:
   REMOTE-USER: joe.smith

website/sidebars.js

@@ -12,7 +12,8 @@ module.exports = {
             type: "category",
             label: "Users & Groups",
             items: [
-                "user-group/user"
+                "user-group/user",
+                "user-group/group",
             ]
         },
         {