Update locator example in README
Update locator example in README

Either

```ruby
class Page
  include Watirsome
  body :body
end

page = Page.new(@browser)
page.body_body
```

or

```ruby
class Page
  include Watirsome
  element :body, tag_name: 'body'
end

page = Page.new(@browser)
page.body_element
```

works correctly.

p0deje/watirsome,p0deje/watirsome