contributing a new plugin [skip ci]

experimental/babel-preset-env/CONTRIBUTING.md

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+## Contributing
+
+### Adding a new plugin to support (when approved in the next ECMAScript version)
+
+#### Update [`pluginFeatures.js`](/data/pluginFeatures.js)
+
+Example:
+
+In you were going to add `**` which is in ES2016:
+
+Find the relevant entries on [compat-table](kangax.github.io/compat-table/):
+
+`exponentiation (**) operator`
+
+Find the corresponding babel plugin: 
+
+`transform-exponentiation-operator`
+
+Add add them in this structure:
+
+```js
+// es2016
+"transform-exponentiation-operator": {
+  features: [
+    "exponentiation (**) operator",
+  ],
+},
+ ```
+ 
+#### Update [`plugins.json`](/data/plugins.json)
+
+Until `compat-table` is a standalone npm module for data we are using the git url
+
+`"compat-table": "github:kangax/compat-table#gh-pages",`
+
+So we update and then run `npm run build-data`. If there are no changes, then `plugins.json` will be the same.