add DevTools in Preview note (#289)

Author: bundyo

content/docs/en/getting-started/1-quick-start.md

@@ -36,3 +36,6 @@ This set of commands performs the following operations on your system:
 4. Installs any npm dependencies locally.
 5. If executing `tns preview`, produces a QR code which can be used to preview the app on a device.
 6. If executing `tns run`, builds and runs the project on all connected devices or in native emulators.
+
+**Note**: If you choose to install DevTools, you won't be able to use `tns preview`, as the Preview app
+doesn't support one of the plugins DevTools uses.