Merge pull request facebook#149 from JReinhold/doc_migration_to_2.5.0

added migration steps to v2.5.0

README.md

@@ -21,6 +21,26 @@ When you run `npm run build` the terminal will output the error, including the h
 
 ![CodeHighlight](https://cloud.githubusercontent.com/assets/175278/22310149/1ee66ccc-e346-11e6-83ff-e3a053701fb4.gif)
 
+## Migration
+
+In general, most upgrades won't require any migration steps to work, but if you experience problems after an upgrade, please file an issue, and we'll add it to the list of migration steps below.
+
+### From `<2.5.0` to `>=2.5.0`
+
+Version `2.5.0` introduces a new config file for jest, that is necessary for the tests to run. If you were previously running a version older than `v2.5.0` and upgraded to `v2.5.0` or newer, you need to manually add the new file, or else you'll get an error similar to this when trying to run your tests:
+
+```javascript
+Test suite failed to run
+
+{
+    "messageText": "Cannot read file 'C:\\[project]\\tsconfig.test.json': ENOENT: no such file or directory, open 'C:\\[project]\\tsconfig.test.json'.",
+    "category": 1,
+    "code": 5012
+}
+```
+
+To fix this, create a new file *in the root of the project* called `tsconfig.test.json`, and paste [the content of this file into it](https://raw.githubusercontent.com/wmonk/create-react-app-typescript/master/packages/react-scripts/template/tsconfig.test.json). Everything should work now. For more info, please see [this issue](https://github.com/wmonk/create-react-app-typescript/issues/141).
+
 ## Changelog
 
 ### 2.6.0