feat(sterni/acme/plan9port): set (rough) location for astro(1)

I semi regularly look up the sunset time, so this is actually useful for
me. Time zone conversion seems to be broken which I'll have to debug.
The GMT sunset times it comes up with seem to be accurate, though.

Change-Id: If179f9e1bb56665d4d6f8b0f81272d3d74fe6cec
Reviewed-on: https://cl.tvl.fyi/c/depot/+/13101
Tested-by: BuildkiteCI
Autosubmit: sterni <sternenseemann@systemli.org>
Reviewed-by: sterni <sternenseemann@systemli.org>

users/sterni/acme/plan9port/default.nix

@@ -52,6 +52,11 @@ pkgs.plan9port.overrideAttrs (old: {
         '';
   };
 
+  postInstall = ''
+    echo '48.3626 10.9026 483\
+    (OpenLab Augsburg)' > $out/plan9/sky/here
+  '';
+
   doInstallCheck = true;
   installCheckPhase = old.installCheckPhase or "" + ''
     export NAMESPACE="$(mktemp -d)"