README.md of src/bridges (recommendation)

[santiagoclv]

This is only a recommendation:

I have been using your wisper-rcp IframeBridge (it is awesome) to communicate with iframes that are mounted on my app, after a couple of times mounting and umounting iframes, the device where I run the app start suffer by lack of memory, the problem was a leak of memory induced because I was not closing the bridges (bidge.close())

I would suggest to add something about close( ) to the Readme.md on src/bridges

Thanks!
Santiago.