Adds details to main configuration documentation on what happens to mime type filtering when a request's mime type is not matched by any of the rules in the share option.
Lifts example from the 1.24.0 news item for usage with a fallback option.
Tested locally to make sure formatting and reference links work and go the correct places.
Same as https://github.com/nginx/unit-docs/pull/66, but from my own fork instead of a different branch from the same unit-docs repository.
Closes #63
Tested locally to make sure formatting and reference links work and go the correct places.