Show a link to ConanCenterIndex issues when a library is missing

When looking for a library in the search, and that library is not listed/missing the output is almost unhelpful:

It shows Recipes 0, but does not give advice on how to continue in case wanting this library available.

It would be nice to have a text message with a link to Conan Center Index issues, where people can request the missing library:

```
Package not found in Conan Center. To request it, please file an issue at [Conan Center Index](https://github.com/conan-io/conan-center-index/issues).
```