[doc] custom_models: mention security features of the Hub
 cc @McPatate @n1t0 and  @SBrandeis @osanseviero and everyone reading this, don't hesitate to regularly read the doc and create links between the hub doc and the libraries docs
_The documentation is not available anymore as the PR was closed or merged._<|||||>your last change @stevhliu looks good to me, ready to merge for everyone?