issue #116: add example of 'Browser#position' into README.md

Author: Mifrill

README.md

@@ -234,6 +234,14 @@ browser.go_to("https://github.com/")
 browser.stop
 ```
 
+#### position
+
+Set the position for the browser window bounds
+
+```ruby
+browser.position = { left: 10, top: 20 }
+browser.position # => [10, 20]
+```
 
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