Migrate from DockerHub to ghcr.io (#16)

* Migrate from DockerHub to GHCR.

* Remove branch trigger, update README.

.github/workflows/build-push-dockerhub.yaml

@@ -10,21 +10,10 @@ jobs:
   docker:
     runs-on: ubuntu-latest
     steps:
-      - name: Set up QEMU
-        uses: docker/setup-qemu-action@v2
+      - uses: actions/checkout@v2
 
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v2
-
-      - name: Login to Docker Hub
-        uses: docker/login-action@v2
-        with:
-          username: ${{ secrets.DOCKERHUB_USERNAME }}
-          password: ${{ secrets.DOCKERHUB_TOKEN }}
-
-      - name: Build and push
-        uses: docker/build-push-action@v4
+      - name: Build and publish Docker image for ${{ github.repository }}
+        uses: macbre/push-to-ghcr@master
         with:
-          push: true
-          tags: ${{ vars.DOCKERHUB_TAG }}
-
+          image_name: ${{ github.repository }}
+          github_token: ${{ secrets.GITHUB_TOKEN }}

README.md

@@ -90,7 +90,7 @@ go build cmd/bom_exporter.go
 A binary called `bom_exporter` should be compiled.
 
 ## Docker
-A Docker image is available on Docker Hub [here](https://hub.docker.com/r/gkoh0/bom_exporter).
+A Docker image is available on ghcr.io [here](https://github.com/gkoh/bom_exporter/pkgs/container/bom_exporter).
 
 ## Test
 ```