Update hmr.md (#507)

* Update hmr.md

* Update src/i18n/en/docs/hmr.md

Co-Authored-By: Niklas Mischkulnig <mischnic@users.noreply.github.com>

src/i18n/en/docs/hmr.md

@@ -1,6 +1,14 @@
 # 🔥 Hot Module Replacement
 
-Hot Module Replacement (HMR) improves the development experience by automatically updating modules in the browser at runtime without needing a whole page refresh. This means that application state can be retained as you change small things. Parcel's HMR implementation supports both JavaScript and CSS assets out of the box. HMR is automatically disabled when bundling in production mode.
+Hot Module Replacement (HMR) improves the development experience by automatically updating modules in the browser at runtime without needing a whole page refresh. This means that application state can be retained as you change small things. Parcel's HMR implementation supports both JavaScript and CSS assets.
+
+As of version 1.12.0, the default implementation has changed to fully refresh the page when files change. You can opt-in to enable true HMR by adding the following in your app. This will only apply in development; HMR is automatically disabled when bundling in production mode.
+
+```javascript
+if (module.hot) {
+  module.hot.accept()
+}
+```
 
 As you save files, Parcel rebuilds what changed and sends an update to any running clients containing the new code. The new code then replaces the old version, and is re-evaluated along with all parents. You can hook into this process using the `module.hot` API, which can notify your code when a module is about to be disposed, or when a new version comes in. Projects like [react-hot-loader](https://github.com/gaearon/react-hot-loader) can help with this process, and work out of the box with Parcel.