Add 0.4.0 changelog

CHANGELOG.md

+## 0.4.0 (September 2, 2016)
+
+### Build Dependency (`react-scripts`)
+
+* **Breaking Change:** Disabled implicit serving of source files in development. ([@gaearon](https://github.com/gaearon) in [#551](https://github.com/facebookincubator/create-react-app/pull/551))
+* You can use `NODE_PATH` environment variable for absolute `import` paths. ([@jimmyhmiller](https://github.com/jimmyhmiller) in [#476](https://github.com/facebookincubator/create-react-app/pull/476))
+* If `src/setupTest.js` exists, it will be used to setup the test environment. ([@gaelduplessix](https://github.com/gaelduplessix) in [#548](https://github.com/facebookincubator/create-react-app/pull/548))
+* If `HTTPS` environment variable is set to `true`, development server will run in HTTPS mode. ([@dceddia](https://github.com/dceddia) in [#552](https://github.com/facebookincubator/create-react-app/pull/552))
+
+### Migrating from 0.3.1 to 0.4.0
+
+Inside any created project that has not been ejected, run:
+
+```
+npm install --save-dev --save-exact react-scripts@0.3.1
+```
+
+### Breaking Change in 0.4.0
+
+Paths like `/src/somefile.png` used to be served in development, but only by accident. They never worked in production builds. Since 0.4.0, we [don’t serve static files by default in development anymore either](https://github.com/facebookincubator/create-react-app/pull/551). This removes a dangerous inconsistency that we never intentionally supported.
+
+If you need a static file to be part for the build, [import it from JavaScript and you will get its filename](https://github.com/facebookincubator/create-react-app/blob/master/template/README.md#adding-images-and-fonts). This ensures it gets included into the production build as well, and its filename contains the content hash.
+
+If you used static files with `<link href>`, [read this new guide](https://github.com/facebookincubator/create-react-app/blob/master/template/README.md#referring-to-static-assets-from-link-href) on how to make sure these files get included into the builds. For example, you can replace `<link href="/src/favicons/favicon-32.png">` with `<link href="./src/favicons/favicon-32.png">`, and then Webpack will recognize it and include it into the build.
+
+If you referenced some other files from `index.html`, please file an issue to discuss your use case. In the meantime, you can serve them from a separate static server until your use case is supported.
+
 ## 0.3.1 (September 2, 2016)
 
 ### Build Dependency (`react-scripts`)