Add help text describing how to avoid explicit sizing of icons in theme_languageicons_icon

Hi,

I have a bilingual site with two flags with different aspect ratios. When looking at the admin interface I couldn't see how to configure languageicons not to set an explicit size. By inspecting the code I saw that if I omitted the Image size value altogether, it would be omitted in the theme function. It might be good to add some words to that effect after the help text Image size for language icons, in the form "width x height".

Thanks,

Andy