Update changeset & documentation

Signed-off-by: Philipp Hugenroth <philipph@spotify.com>

.changeset/stale-brooms-fry.md

@@ -2,4 +2,50 @@
 '@backstage/create-app': patch
 ---
 
-// TODO
+You can now add `SidebarGroups` to the current `Sidebar`. This will not affect how the current sidebar is displayed, but allows a customization on how the `MobileSidebar` on smaler screens will look like. A `SidebarGroup` wil be displayed with the given icon in the `MobileSidebar`.
+
+A `SidebarGroup` can either link to an existing page (e.g. `/search` or `/settings`) or wrap components, which will be displayed in a full screen overlay menu (e.g. `Menu`).
+
+```diff
+<Sidebar>
+    <SidebarLogo />
++   <SidebarGroup label="Search" icon={<SearchIcon />} to="/search">
+        <SidebarSearchModal />
++   </SidebarGroup>
+    <SidebarDivider />
++   <SidebarGroup label="Menu" icon={<MenuIcon />}>
+        <SidebarItem icon={HomeIcon} to="catalog" text="Home" />
+        <SidebarItem icon={CreateComponentIcon} to="create" text="Create..." />
+        <SidebarDivider />
+        <SidebarScrollWrapper>
+            <SidebarItem icon={MapIcon} to="tech-radar" text="Tech Radar" />
+        </SidebarScrollWrapper>
++   </SidebarGroup>
+    <SidebarSpace />
+    <SidebarDivider />
++   <SidebarGroup
++       label="Settings"
++       icon={<UserSettingsSignInAvatar />}
++       to="/settings"
++   >
+        <SidebarSettings />
++   </SidebarGroup>
+</Sidebar>
+```
+
+Additionally you can order the groups differently in the `MobileSidebar` than in the usual `Sidebar` simply by giving a group a priority. The groups will be displayed in a descending order from left to right.
+
+```diff
+<SidebarGroup
+    label="Settings"
+    icon={<UserSettingsSignInAvatar />}
+    to="/settings"
++   priority={1}
+>
+    <SidebarSettings />
+</SidebarGroup>
+```
+
+If you decide against adding `SidebarGroups` to your `Sidebar` the `MobileSidebar` will contain one default menu item, which will open a full screen overlay menu displaying all of the content of the current `Sidebar`.
+
+More information on the `SidebarGroup` & the `MobileSidebar` component can be found in the changeset for the `core-components`.