feat: add a dockerfile

Signed-off-by: David Mehren <git@herrmehren.de>

docker/README.md

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+<!--
+SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
+# Using HedgeDoc with Docker
+
+**Important:** This README does **not** refer to HedgeDoc 1. For setting up HedgeDoc 1 with Docker, see https://docs.hedgedoc.org/setup/docker/.
+
+The `Dockerfile` in this repo uses multiple stages and can be used to create both images for development
+and images with only production dependencies.
+It uses features which are only available in BuildKit - see https://docs.docker.com/go/buildkit/ for more information.
+
+## Build a production image
+**Note:** This does not include any frontend!
+
+To build a production image, run the following command *from the root of the repository*:  
+`docker build -t hedgedoc-prod -f docker/Dockerfile .`
+
+When you run the image, you need to provide environment variables to configure HedgeDoc.
+See [the config docs](../docs/content/config/index.md) for more information.
+This example starts HedgeDoc on localhost, with non-persistent storage:  
+`docker run -e HD_DOMAIN=http://localhost -e HD_MEDIA_BACKEND=filesystem -e HD_MEDIA_BACKEND_FILESYSTEM_UPLOAD_PATH=uploads -e HD_DATABASE_DIALECT=sqlite -e HD_DATABASE_STORAGE=hedgedoc.sqlite -e HD_SESSION_SECRET=foobar -e HD_LOGLEVEL=debug -p 3000:3000 hedgedoc-prod`
+
+
+## Build a development image
+You can build a development image using the `development` target:  
+`docker build -t hedgedoc-dev -f docker/Dockerfile --target development .`
+
+You can then, e.g. run tests inside the image:  
+`docker run hedgedoc-dev yarn run test:e2e`