Display README.md if default module has no moduleDoc

Now that we are displaying a doc view by default, a lot of modules don't have good JSDoc. While this has been the standard for Rust and Go, that a lack of inline docs generates "bad" display of information we need to evolve towards that.

For example https://deno.land/x/dejs, the 10th most popular module, is just confusing to a user.

Currently if a module doesn't have a default module we display the README after the directory listing.

I propose if the default module doesn't have moduleDoc that we display the README after the symbol list.

@crowlKats we just need to figure out if you want apiland to figure that out for you or not. While it wouldn't deliver the content, it could provide a flag/prop with a reference to the README.md, might want that for the index too.