Adds dev container and docs (#1499)

ci/dev-image/Dockerfile

+FROM node:12
+
+RUN apt-get update && apt-get install -y \
+    curl \
+    iproute2 \
+    vim \
+    iptables \
+    net-tools \
+    libsecret-1-dev \
+    libx11-dev \
+    libxkbfile-dev
+
+CMD ["/bin/bash"]

ci/dev-image/exec.sh

+#!/usr/bin/env bash
+# exec.sh opens an interactive bash session inside of a docker container
+# for improved isolation during development
+# if the container exists it is restarted if necessary, then reused
+
+set -euo pipefail
+cd "$(dirname "$0")"
+
+# Ensure submodules are cloned and up to date.
+git submodule update --init
+
+container_name=code-server-dev
+
+enter() {
+  echo "--- Entering $container_name"
+  docker exec -it $container_id /bin/bash
+}
+
+run() {
+  echo "--- Spawning $container_name"
+  container_id=$(docker run \
+    -it \
+    --name $container_name \
+    "-v=$PWD:/code-server" \
+    "-w=/code-server" \
+    "-p=127.0.0.1:8080:8080" \
+    $([[ -t 0 ]] && echo -it || true) \
+    $container_name)
+}
+
+build() {
+  echo "--- Building $container_name"
+  cd ../../
+  docker build -t $container_name -f ./ci/dev-image/Dockerfile . > /dev/null
+}
+
+container_id=$(docker container inspect --format="{{.Id}}" $container_name 2> /dev/null) || true
+
+if [ "$container_id" != "" ]; then
+  echo "-- Starting container"
+  docker start $container_id > /dev/null
+
+  enter
+  exit 0
+fi
+
+build
+run
+enter

doc/CONTRIBUTING.md

@@ -10,6 +10,16 @@ yarn vscode
 yarn watch # Visit http://localhost:8080 once completed.
 ```
 
+To develop inside of an isolated docker container:
+
+```shell
+./ci/dev-image/exec.sh
+
+root@12345:/code-server# yarn
+root@12345:/code-server# yarn vscode
+root@12345:/code-server# yarn watch
+```
+
 Any changes made to the source will be live reloaded.
 
 If changes are made to the patch and you've built previously you must manually