scrapy tutorial - add step for creating __init__.py

After going through the tutorial and trying to run the scraper, I was getting "unable to import" errors on the config file (no module with name scraper_app.settings). finally, I found that I needed an **init**.py in the scraper_app (and subsequently, upon another error, also in spiders directory). I am still investigating that issue for myself but am thinking those should be in the tutorial.