move devcontainer definition (#31)

.devcontainer.json

@@ -8,6 +8,7 @@
     "WORKSPACE_DIRECTORY": "${containerWorkspaceFolder}"
   },
   "extensions": ["timonwong.shellcheck", "esbenp.prettier-vscode"],
+  "mounts": ["type=volume,target=/var/lib/docker"],
   "settings": {
     "terminal.integrated.profiles.linux": {
       "zsh": {