Add devcontainer

.devcontainer/Dockerfile

@@ -0,0 +1,10 @@
+# See here for image contents: https://github.com/microsoft/vscode-dev-containers/tree/v0.245.2/containers/ubuntu/.devcontainer/base.Dockerfile
+
+# [Choice] Ubuntu version (use ubuntu-22.04 or ubuntu-18.04 on local arm64/Apple Silicon): ubuntu-22.04, ubuntu-20.04, ubuntu-18.04
+ARG VARIANT="jammy"
+FROM mcr.microsoft.com/vscode/devcontainers/base:0-${VARIANT}
+
+RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get -y install --no-install-recommends direnv
+
+