Add fixed block on where to report issues

[karmatosed]

This is an awesome resource and as a result bugs may be found. There are a few things we could maybe do with a little block that can't be removed.

• Mention where to report Gutenberg bugs.
• Mention to test in non Frontendberg install any bug you find, just incase there's a difference.
• Mention to report here if it's a Frontendberg bug.

[tomjn]

The widget and nav menu screen work means this is a high priority now, if only to provide a way to navigate between screens

[tomjn]

It looks like editorskit used Frontenberg and implemented this but didn't contribute back :(