Breaking Change (v0.11.0): update security policy for web components

[wwwillchen]

We've just released https://github.com/google/mesop/releases/tag/v0.11.0 which changed how JavaScript modules for web components are loaded (#723) so you may need to update your security policy. There's improved error messages in the terminal: #724 and improved troubleshooting docs

Please feel free to file an issue if you run into any issues - thanks.