Doc: add unpkg to connect-src instruction for the icon component

[alizedebray]

When using the post-icon component, icons are retrieved from https://unpkg.com/ therefore the URL should be added to the connect-src in index.html. This should be aded to the documentation.

[oliverschuerch]

Please ask Remy van Hoof to add this information to the blueprint.

[pazoozooCH]

I was having issues with this (I think). I couldn't get version 1.3.5 working whatever I tried (maybe a bugged version)?
With version 1.3.6, it seems to be enough to add unpkg.com to img-src, like

  <meta http-equiv="Content-Security-Policy"
        content="default-src 'none';
               script-src 'self' 'unsafe-eval';
               style-src 'self' 'unsafe-inline';
               img-src 'self' https://web.post.ch https://unpkg.com data: 'self' *.pnet.ch *.post.ch;
               connect-src 'self';
               form-action 'self';
               base-uri 'self';
               font-src 'self' https://fonts.post.ch data: 'self'">

@alizedebray , you're writing of connect-scr, is there something I'm missing?`

Cheers Martin