Fix curly brace

The property declarations do not go in the braces of a class extension. They lie in-between the interface and it's ending declaration.
Fix another curly brace and atomic v nonatomic

Note: Propertyatomicityisnotsynonymouswithanobject’sthreadsafety.
Consider an XYZPerson object in which both a person’s first and last names are changed using atomic accessors from one thread. If another thread accesses both names at the same time, the atomic getter methods will return complete strings (without crashing), but there’s no guarantee that those values will be the right names relative to each other. If the first name is accessed before the change, but the last name is accessed after the change, you’ll end up with an inconsistent, mismatched pair of names.
This example is quite simple, but the problem of thread safety becomes much more complex when considered across a network of related objects. Thread safety is covered in more detail in Concurrency Programming Guide .
Update README.md

fixed spelling and removed the extra wordiness.
Concurrency vs. atomicy is always a tough one...
Merge pull request #7 from blaalz/master

Fix curly brace and update atomicity