#6045 add Ubuntu 20.04 compatible Docker image

docker/ubuntu-2004-nightly/Dockerfile

@@ -0,0 +1,16 @@
+FROM ubuntu:20.04
+
+RUN apt-get update --fix-missing
+RUN apt-get upgrade --yes
+RUN apt-get install --yes \
+    wget \
+    libc-dev \
+    binutils \
+    build-essential \
+    clang
+RUN wget -q -O roc.tar.gz https://github.com/roc-lang/roc/releases/download/nightly/roc_nightly-linux_x86_64-latest.tar.gz
+RUN mkdir /usr/lib/roc
+# --strip-components=1 not needed once https://github.com/roc-lang/roc/issues/4118 is solved.
+RUN tar -xvz -f roc.tar.gz --directory /usr/lib/roc --strip-components=1
+
+ENV PATH="$PATH:/usr/lib/roc"

docker/ubuntu-2004-nightly/docker-compose.example.yml

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+version: "3"
+services:
+  roc:
+    build: .
+    entrypoint: roc
+    working_dir: /home/ubuntu/app
+    volumes:
+      - ../../:/home/ubuntu/app