provide list of open source projects as reference

Adapting conan is easier when users have real-world projects to look at.

I'm currently playing with conan 2 and would like to see some real-world apps using conan 2. I've been in this situation in the past when trying out conan features.

The conan-center-index repository is a good place for referencing repackaged libraries. What I'm looking for are open source libraries and apps that are using conan.

The list could go either into the docs or be added to the "OUR USERS" display on conan.io

If I find some popular projects, I'll add them to this issue.

| Project | Type | Conan Version |
| -- | -- | -- |
| [google/flatbuffers](https://github.com/google/flatbuffers/tree/master) | Library | 1 |
| [google/fruit](https://github.com/google/fruit/blob/master/conanfile.py) | Library | 1 |
| [google/orbit](https://github.com/google/orbit/tree/main) | App | 1 |