Doc update for unpkg src attr

[cavemansspa]

No description provided.

[orbitbot]

AFAIK (without checking) this is intentional and should not require a change.

[orbitbot]

After checking, this works as intended as long as the file is being served through any development server, and not opened directly as a file. Perhaps rather update the documentation to state that.

[pygy]

Thanks @cavemansspa.

@orbitbot It doesn't hurt, if only to prevent man in the middle attacks while developing locally (stuff like bad public proxies/access points that inject code in unencrypted content).