Update doc, add .gitignore and recommended vscode extension (#3)

* Add hadolint to recommended vscode extensions

* Add Action publish-docker-image.yml

Author: tschaffter

.github/workflows/ci.yml

@@ -11,9 +11,7 @@ jobs:
     runs-on: ubuntu-18.04
 
     steps:
-    # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
     - uses: actions/checkout@v2
 
-    # Runs a single command using the runners shell
     - name: Run builder script with arguments `--help`
       run: ./build-kernel.sh --help

.github/workflows/publish-docker-image.yml

@@ -0,0 +1,23 @@
+name: Publish Docker Image
+
+# on:
+#   push:
+#     branches: [ master, develop ]
+#   pull_request:
+#     branches: [ master, develop ]
+
+jobs:
+  publish-docker-image:
+    runs-on: ubuntu-18.04
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Publish Docker image
+      uses: docker/build-push-action@v1
+      with:
+        username: ${{ secrets.DOCKER_USERNAME }}
+        password: ${{ secrets.DOCKER_PASSWORD }}
+        repository: tschaffter/${{ github.event.repository.name }}
+        tag_with_ref: true
+        push: ${{ startsWith(github.ref, 'refs/tags/') }}

.gitignore

@@ -0,0 +1 @@
+output/

.vscode/extensions.json

@@ -0,0 +1,5 @@
+{
+    "recommendations": [
+      "exiasr.hadolint"
+    ]
+}

README.md

@@ -56,10 +56,11 @@ Check the above documentation to make sure that these examples are up-to-date.
 ### Cross-compile the kernel
 
 The command below builds the branch `rpi-4.19.y` for the Raspberry Pi 4
-(`bcm2711_defconfig`). Because this branch is not stable, we include today's
-date to the value of `--kernel-localversion` (`4.19.y-20200614-hardened`).
+(`bcm2711_defconfig`). Because this branch is in progress, we include today's
+date to the value of `--kernel-localversion` (`4.19.y-20200614-hardened`). You
+can set the value of `--kernel-localversion` to anything you want.
 
-Once installed, the full kernel name will be
+Once installed, the full kernel name will be:
 
 ```console
 $ uname -a
@@ -105,7 +106,7 @@ Copy the Debian packages `$PWD/output/*.deb` to the target Raspbery Pi, for
 example using `scp`, then follow the instructions given at the end of the build
 command.
 
-## Notes
+## Customize your build
 
 - The builder uses all the CPU cores available to the Docker container. By default,
 that is all the CPU cores of the host. Use
@@ -120,7 +121,7 @@ a different toolchain and kernel source code.
 
 ```console
 $ git clone <toolchain-repo> tools
-$ git cllone <kernel-repo> linux
+$ git clone <kernel-repo> linux
 $ docker run \
     --rm \
     -v $PWD/output:/output \