update docs

README.md

@@ -107,6 +107,16 @@ After [initialization](#initialization), Rustlings can be launched by simply run
 This will start the _watch mode_ which walks you through the exercises in a predefined order (what we think is best for newcomers).
 It will rerun the current exercise automatically every time you change the exercise's file in the `exercises/` directory.
 
+You can specify an editor command with the `--editor` option to open exercises directly from watch mode:
+
+```bash
+rustlings --editor code     # For VS Code
+rustlings --editor vim      # For Vim
+rustlings --editor "code --wait" # For VS Code with wait option
+```
+
+Then press `e` in watch mode to open the current exercise in your editor.
+
 <details>
 <summary><strong>If detecting file changes in the <code>exercises/</code> directory fails…</strong> (<em>click to expand</em>)</summary>