Suggestion: Add notes about .none()

[ydakuka]

I suggest to add paragraph about using method .none().

Let's say we have the following samples:

User.where(id: nil)
User.where(id: 0)
User.where(id: [])
User.where(id: {})
User.limit(nil)
User.limit(0)

All these lines can be replaced with the code:

User.none

[andyw8]

Are those other approaches common? Perhaps you could check on https://github.com/eliotsykes/real-world-rails