Actions: Add Cachix auth token instructions

.github/workflows/build.yml

@@ -24,8 +24,9 @@ jobs:
         # Format: Your cachix cache host name without the ".cachix.org" suffix.
         # Example: mycache (for mycache.cachix.org)
         #
-        # For this to work, you also need to set the CACHIX_SIGNING_KEY secret
-        # in your repository settings in Github found at https://github.com/<your_githubname>/nur-packages/settings/secrets
+        # For this to work, you also need to set the CACHIX_SIGNING_KEY or
+        # CACHIX_AUTH_TOKEN secret in your repository settings in Github found
+        # at https://github.com/<your_githubname>/nur-packages/settings/secrets
         cachixName:
           - <YOUR_CACHIX_NAME>
         nixPath:
@@ -49,6 +50,8 @@ jobs:
       with:
         name: ${{ matrix.cachixName }}
         signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
+        # or:
+        #authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
     - name: Check evaluation
       run: |
         nix-env -f . -qa \* --meta --xml \