add --recursive to sass watch script (#1564)

Author: Alessandro Burato

packages/react-scripts/template/README.md

@@ -419,7 +419,7 @@ Then we can change `start` and `build` scripts to include the CSS preprocessor c
 ```diff
    "scripts": {
      "build-css": "node-sass src/ -o src/",
-     "watch-css": "npm run build-css && node-sass src/ -o src/ --watch",
+     "watch-css": "npm run build-css && node-sass src/ -o src/ --watch --recursive",
 -    "start": "react-scripts start",
 -    "build": "react-scripts build",
 +    "start-js": "react-scripts start",