feat: idols & nix's distributed building

hosts/idols/README.md

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+# Oshi no Ko
+
+These four servers are named after the four main characters of the mange/anime Oshi no Ko, they form a NixOS distributed building cluster,
+I usually run the build command on `Ai` and nix will distribute the build to other three machines, which is convenient and fast.
+
+When building some packages for riscv64 or aarch64, I often have no cache available because of various changes under the hood, so I need to build much more packages than usual, which is one of the reasons why the cluster was originally built, and another reason is distributed building is cool!
+
+![](./_img/nix-distributed-building.webp)
+
+![](./_img/nix-distributed-building-log.webp)
+
+## References
+
+See [Oshi no Ko 【推しの子】 - Wikipedia](https://en.wikipedia.org/wiki/Oshi_no_Ko) for more information.