Is there a way to add food from restaurants

For some restaurants yes. But be careful with what you find. Some as grobangal says are just in the database. Others can be gotten from the mobile app by clicking on the simple to the left of the bar code (the one you find on map apps). That will give you a list of restaurants nearby. If it's a chair, it may be in the database. If it's not in the database you can request it. Hit or miss, really. A combination of that, what grobangal says, and using estimation are your best bets.

See here:
http://blog.myfitnesspal.com/myfitnesspal-introduces-restaurant-logging/