improve github app documentation (#344)

you have to use the generated token with the checkout step as well otherwise the source repository isn't readable.

Signed-off-by: Marvin Osswald <88089002+marvin-belonio@users.noreply.github.com>
Co-authored-by: andy Augustin <AndreasAugustin@users.noreply.github.com>

README.md

@@ -103,6 +103,7 @@ If your current repository was created from a private template, there are severa
 
 You can create and use a [GitHub App][github-app] to handle the access to the private template repository.
 To generate a token for your app you can use a separate action like [tibdex/github-app-token][github-app-token].
+You have to setup the checkout step with the generated token as well.
 
 ```yaml
 jobs:
@@ -116,7 +117,10 @@ jobs:
  with:
  app_id: ${{ secrets.APP_ID }}
  private_key: ${{ secrets.PRIVATE_KEY }}
-
+ - name: Checkout
+ uses: actions/checkout@v3
+ with:
+ token: ${{ steps.generate_token.outputs.token }}
  - name: actions-template-sync
  uses: AndreasAugustin/actions-template-sync@v0.8.0
  with: