Added food basket pinboard warning

What does this MR do?

Add warning to food baskets. Reasons: A lot of food baskets don't get picked up. I would like to disable comment in general. This is a first step in this direction.

I am happy about text suggestions / changes!

How confident are you it won't break things if deployed?

Should work

Links to related issues

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))