Update for creating and modifying the view for Picture Gallery

I have spend some time before I figured out how to use the Picture Url Helpers for pictures from Picture Gallery. I think this information will be very useful in the guide for the newcomers.
Minor correction: Render picutre gallery

There should be :size instead of :image_size
Minor: typo correction in create_elements.yml

Minor: typo correction in create_elements.yml
Merge pull request #3 from matfiz/master

Useful info about rendering a custom view for Picture Gallery