docs(tmux): add scroll mode shortcuts

Author: rafaelrinaldi

tmux/README.md

@@ -49,6 +49,8 @@
 | `<Prefix> x` | Destroy pane |
 | `clear` or `Ctrl+l` | Clear current pane output (equivalent to <kbd>⌘</kbd> + <kbd>K</kbd>) |
 | `<Prefix> r` | Render UI |
+| `<Prefix> [` | Enter scroll mode |
+| `q` | Exit scroll mode |
 
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