Update devcontainer.json

.devcontainer/devcontainer.json

@@ -15,6 +15,7 @@
 		"python.pythonPath": "/usr/local/bin/python",
 		"python.linting.pylintEnabled": true,
 		"python.linting.enabled": true,
-		"files.trimTrailingWhitespace": true
+		"files.trimTrailingWhitespace": true,
+		"editor.rulers": [80]
 	}
 }