doc/faq: add example setups

Author: astro

doc/src/faq.md

@@ -1,5 +1,14 @@
 # Frequently Asked Questions
 
+## Are there elaborate example setups?
+
+microvm.nix is used in these open-source infrastructure projects:
+
+- [C3D2 services](https://gitea.c3d2.de/c3d2/nix-config)
+- [DD-IX services](https://github.com/dd-ix/nix-config)
+
+Let us know if you know more!
+
 ## Can I support the development and maintenance of this project?
 
 [❤ Sponsor](https://github.com/sponsors/astro)