Add ci, update README add dockerignore.

.dockerignore

@@ -0,0 +1,2 @@
+ci/
+README.md

README.md

@@ -0,0 +1,16 @@
+# concourse-buildkit
+
+A docker image to build multiarch images on [concourse](https://concourse-ci.org)
+since buildx is flakey for me.
+
+Currently only the docker registry is supported.
+
+
+## parameters
+
+- username: Optional. The username used to log into the registry.
+- password: Optional. The password used to log into the registry.
+
+## Example
+
+To view a simple invocation just look at [pipeline.yml](/ci/pipeline.yml).

ci/pipeline.yml

@@ -0,0 +1,41 @@
+---
+resources:
+- name: source
+  type: git
+  source:
+    uri: https://gitea.redxef.at/redxef/concourse-buildkit
+    branch: master
+
+jobs:
+- name: build-push
+  plan:
+  - get: source
+    trigger: true
+  - task: build
+    privileged: true
+    config:
+      platform: linux
+      image_resource:
+        type: registry-image
+        source:
+          repository: redxef/concourse-buildkit
+      inputs:
+      - name: source
+        path: .
+      params:
+        username: ((docker.username))
+        password: ((docker.password))
+      run:
+        path: entrypoint.sh
+        args:
+        - build
+        - --frontend
+        - dockerfile.v0
+        - --local
+        - context=.
+        - --local
+        - dockerfile=.
+        - --opt
+        - platform=aarch64,arm,ppc64le,s390x,x86_64
+        - --output
+        - type=image,name=docker.io/redxef/concourse-buildkit,push=true