Link to Twig extensions is broken

[mpdude]

At the very end of https://github.com/symfony/symfony-docs/blob/master/reference/twig_reference.rst, a reference is made to "the official Twig Extensions documentation".

This link to http://twig.sensiolabs.org/doc/extensions/index.html is broken.

I don't know for sure, but presume it is intended to point here: https://github.com/twigphp/Twig-extensions

Additionally, is there a default/recommended Symfony Bundle to hook up these extensions in the Framework?

[mpdude]

See #7612 and #7613 for suggested fixes