feat: add note on Cachix binary cache

This fixes the request in #25.

README.md

@@ -8,11 +8,32 @@ Among other things this includes:
 - derivations to build the seL4 kernel
 - derivations to build our ongoing seL4-rs project, a Rust based wrapper arround seL4
 - derivations to build the seL4-test suite for various (simulated and phyiscal) targets
-- a generic [FOD](https://nixos.org/manual/nixpkgs/stable/#fixed-output-derivation) fetcher for [Google's repo tool](https://android.googlesource.com/tools/repo)
+- a generic [FOD](https://nixos.org/manual/nixpkgs/stable/#fixed-output-derivation) fetcher for
+  [Google's repo tool](https://android.googlesource.com/tools/repo)
+
+# Caching
+
+Many of the derivations in this repository depend on huge builds, which are not cached by
+<https://cache.nixos.org/>. To spare you (and us) hours of compiling cross-compilers, the
+CI-pipeline configured for this repository pushes its binary artifacts to the
+[DLR-FT Cachix](https://app.cachix.org/cache/dlr-ft). Hence, you may use the following binary cache
+with [Cachix](https://app.cachix.org):
+`dlr-ft.cachix.org-1:QalYjdLh69S57wX6br7xTVEtOWDoPLXTMTUSurVKnVg=`
+
+To do so, simply invoke the `cachix` executable as followed, before `nix build` or `nix develop`:
+
+```console
+cachix use dlr-ft
+```
+
+Please note: while we try to keep the relevant artifacts in the Cachix, there might be times
+at which some of the artifacts have been evicted from the cache; this is a best-effort to make
+everybody's life easier. There is no guarantee that all (or in fact any) of the dependencies to
+build this repo's derivations is in the cache.
 
 # About code style and DRY
 
-The code especially in the `flake.nix` is very repetetive.
+The code especially in the `flake.nix` is very repetitive.
 This is fully intentional, we want the code to be easily copy-pasteable.
 Nix' expressive syntax would allow for the various things to be condensed into a much shorter generator expression, however, that is detrimental to the goal of this repo:
 providing accessible information on how to compile seL4 related projects in Nix.