Add devcontainer configuration for codespace support (#138)

.devcontainer/docker-compose.yml

@@ -0,0 +1,33 @@
+version: '3.8'
+
+services:
+  app:
+    image: mcr.microsoft.com/devcontainers/typescript-node:latest
+
+    volumes:
+      - ../..:/workspaces:cached
+      
+    # Overrides default command so things don't shut down after the process ends.
+    command: sleep infinity
+
+    # Runs app on the same network as the database container, allows "forwardPorts" in devcontainer.json function.
+    network_mode: service:db
+
+    # Use "forwardPorts" in **devcontainer.json** to forward an app port locally. 
+    # (Adding the "ports" property to this file will not forward from a Codespace.)
+
+  db:
+    image: postgres:latest
+    restart: unless-stopped
+    volumes:
+      - postgres-data:/var/lib/postgresql/data
+    environment:
+      POSTGRES_PASSWORD: 1234
+      POSTGRES_USER: postgres
+      POSTGRES_DB: postgres
+
+    # Add "forwardPorts": ["5432"] to **devcontainer.json** to forward PostgreSQL locally.
+    # (Adding the "ports" property to this file will not forward from a Codespace.)
+
+volumes:
+  postgres-data: