support how can i use an external image host in xenforo 2?

Hi! As I have limited space in my shared hosting account, I want to use external host, 'postimages.org' specifically and this is the javascript code from postimages.org: <script type='text/javascript' src='//mod.postimage.org/zetaboards.js' charset='utf-8'></script> I want to place it as shown...