Update 'README.md'

README.md

@@ -65,7 +65,49 @@ $ npm test
   1 passing (3ms)
 ```
 
-#  Assertions
+# Watch
+
+You can also run eltro in watch mode. Update your package.json and add the following:
+
+```json
+{
+  /* ... */
+  "scripts": {
+    "test": "eltro",
+    "test:watch": "eltro --watch my_watch_name",
+  },
+  "watch": {
+    "my_watch_name": {
+      "patterns": [ "src", "test" ],
+      "extensions": "js,mjs"
+    }
+  },
+  /* ... */
+}
+```
+
+Then add `--watch my_watch_name` to your eltro command (as seen in the above example) and you're good to go:
+
+```bash
+$ npm test:watch
+
+
+  test/test.mjs
+    √ Array #indexOf() should return -1 when value is not present
+
+
+  1 passing (3ms)
+
+[my_watch_name] 09:49:38: Ran successfully. Waiting for file changes before running again...
+```
+
+You can also run your own npm command while using the eltro file watcher like so:
+
+```bash
+$ eltro --watch my_watch_name --npm build
+```
+
+# Assertions
 
 Not only does eltro allow you to use any assertion library of your own choosing, it also comes with it's own assertion library based on node's default [assert](https://nodejs.org/api/assert.html) with a few extra methods: