Updated changeset to minor and added migration instructions

Signed-off-by: Andre Wanlin <awanlin@rapidrtc.com>

.changeset/late-mangos-allow.md

@@ -1,5 +1,28 @@
 ---
-'@backstage/plugin-home': patch
+'@backstage/plugin-home': minor
 ---
 
-Added the HomepageTimer to the new composable Home Page
+The homepage `<Header />` is now part of the composable canvas (allowing you to add the <HomepageTimer />, for example).
+
+You will need to wrap your existing composed `<HomePage />` component in `<Page />`, `<Header />`, and `<Content />` components, like this:
+
+```diff
+// app/src/components/home/HomePage.tsx
+
++ import { Content, Header, Page, HomePageTimer } from '@backstage/core-components';
+
+export const HomePage = () => (
++  <Page themeId="home">
++    <Header title="Home">
++      <HomepageTimer />
++    </Header>
++    <Content>
+  <Grid container spacing={3}>
+    <Grid item xs={12}>
+      <HomePageSearchBar />
+    </Grid>
+    // ...
++    </Content>
++  </Page>
+);
+```