fix alt site title on auth

* Build container image by GitHub Actions

* Trigger docker build only pushed to main branch

* Tweak tagging imgae

- "edge" is the main branch
- "latest" is the tagged latest release

.github/workflows/build-image.yml

@@ -0,0 +1,34 @@
+name: Build container image
+on:
+  push:
+    branches:
+      - "main"
+    tags:
+      - "*"
+jobs:
+  build-image:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: docker/setup-buildx-action@v1
+      - uses: docker/login-action@v1
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - uses: docker/metadata-action@v3
+        id: meta
+        with:
+          images: ghcr.io/${{ github.repository_owner }}/mastodon
+          flavor: |
+            latest=true
+          tags: |
+            type=edge,branch=main
+            type=semver,pattern={{ raw }}
+      - uses: docker/build-push-action@v2
+        with:
+          context: .
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          cache-from: type=registry,ref=ghcr.io/${{ github.repository_owner }}/mastodon:latest
+          cache-to: type=inline

app/views/layouts/auth.html.haml

@@ -12,7 +12,7 @@
         %h2.title.is-2
           = t('auth.login')
 
-        = image_tag asset_pack_path('media/images/bliss/login.jpg'), alt: @instance_presenter.site_title
+        = image_tag asset_pack_path('media/images/bliss/login.jpg'), alt: 'Mastodon Bliss'
 
       .form-container
         = render 'flashes'

lib/tasks/mastodon.rake

@@ -350,11 +350,11 @@ namespace :mastodon do
           end
         end.join("\n")
 
-        generated_header = "# Generated with mastodon:setup on #{Time.now.utc}\n\n"
+        generated_header = "# Generated with mastodon:setup on #{Time.now.utc}\n\n".dup
 
         if incompatible_syntax
-          generated_header << "Some variables in this file will be interpreted differently whether you are\n"
-          generated_header << "using docker-compose or not.\n\n"
+          generated_header << "# Some variables in this file will be interpreted differently whether you are\n"
+          generated_header << "# using docker-compose or not.\n\n"
         end
 
         File.write(Rails.root.join('.env.production'), "#{generated_header}#{env_contents}\n")