Add rtl style rule

[schalkneethling]

@alexgibson r?

[alexgibson]

Worth adding a very short note to the readme on how to use the rtl styling?

[alexgibson]

r+wc :sake:

[schalkneethling]

Yeah, good point. I will add a little something.

[alexgibson]

Could we not use the global dir attribute too perhaps, instead of a custom CSS class name? Just a thought.

https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes

[schalkneethling]

Yes, good call. I found this inside sandstone.less but, much better to use a standard attr if one exists.

[schalkneethling]

@alexgibson updated. Thanks for the suggestions.

[alexgibson]

Looks good other than the last small nit - care to update & squarsh?

[schalkneethling]

@alexgibson squarshed