Call out that --keep-failed with remote builders will keep the failed build directory on that builder

[cole-h]

Motivation

Context

---

Looks something like this:

copying path '/nix/store/cryiszlhhss2h40r3f9m60l92i88m2xd-builder-failing.sh' to 'ssh://localhost'...
note: keeping build directory '/tmp/nix-shell.8G497s/nix-build-failing.drv-16/build'
warning: `--keep-failed` will keep the failed build directory on the remote builder. If the build's architecture matches your host, you can re-run the command with `--builders ''` to disable remote building for this invocation.
error: build of '/nix/store/mqnz9jxm749925bfcgrk0dk5hy5gnz3h-failing.drv' on 'ssh://localhost?remote-store=/tmp/nix-shell.8G497s/nix-test/main/build-remote-input-addressed/machine1?system-features%3Dfoo' failed: Cannot build '/nix/store/mqnz9jxm749925bfcgrk0dk5hy5gnz3h-failing.drv'.
       Reason: builder failed with exit code 1.
       Output paths:
         /nix/store/1g84amb7znczw3213msr5k7l1nkbx7i4-failing

[github-actions]

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