samples/smarthome/local: update README
samples/smarthome/local: update README

- add missing steps
- sync with console changes
- clarify testing instructions
- add troubleshooting

Change-Id: I620dccfe0be975a033099f9e7a8b65be9ad42015

actions-on-google/smart-home-local,actions-on-google/smart-home-local,actions-on-google/smart-home-local