Added More Detail on Init Style

The topic of how our `init` methods are structured recently came up on the team internally, so I thought I'd add our general practice to the guide we do this, because assignment in conditions is just too clever:

````objc
self = [super init];
if (self) {

}
return self;
````

Not this:

````objc
if (self = [super init]) {

}
return self;
````