Opt in to git hooks

.gitignore

@@ -11,3 +11,4 @@ npm-*
 
 # Build
 /build
+/.opt-in

README.md

@@ -32,5 +32,31 @@ Then go to [http://localhost:8601/](http://localhost:8601/) - the playground out
 npm test
 ```
 
+## Git Hooks
+If you would like to ensure your contributions build cleanly every time, opt in
+to the git hooks for the project. Create a file called `.opt-in` in the root of
+the project with the contents:
+
+```
+precommit
+prepush
+postmerge
+postrewrite
+```
+
+Or you can include only the hooks you would like to use.
+
+### precommit
+Run lint before committing
+
+### prepush
+Run tests before pushing
+
+### postmerge
+`npm install` after merging
+
+### postrewrite
+`npm install` after rebasing
+
 ## Donate
 We provide [Scratch](https://scratch.mit.edu) free of charge, and want to keep it that way! Please consider making a [donation](https://secure.donationpay.org/scratchfoundation/) to support our continued engineering, design, community, and resource development efforts. Donations of any size are appreciated. Thank you!

package.json

@@ -11,10 +11,10 @@
     "clean": "rm -rf ./build && mkdir -p build",
     "deploy": "gh-pages -x -r $GH_PAGES_URL -d build -m $DEPLOY_MESSAGE",
     "lint": "eslint .",
-    "postmerge": "npm install",
-    "postrewrite": "npm install",
-    "precommit": "npm run lint",
-    "prepush": "npm run test",
+    "postmerge": "opt --in postmerge --exec 'npm install'",
+    "postrewrite": "opt --in postrewrite --exec 'npm install'",
+    "precommit": "opt --in precommit --exec 'npm run lint'",
+    "prepush": "opt --in prepush --exec 'npm run test'",
     "start": "webpack-dev-server --port $npm_package_config_port --content-base=./build",
     "test": "npm run lint && npm run build"
   },
@@ -41,6 +41,7 @@
     "lodash.bindall": "4.4.0",
     "lodash.defaultsdeep": "4.4.0",
     "minilog": "3.0.1",
+    "opt-cli": "1.5.1",
     "react": "15.x.x",
     "react-dom": "15.x.x",
     "scratch-blocks": "^0.1.0-prerelease",