[PATCH] Documentation: don't repeat configuring the upstream cache

[Valentin Gagarin <valentin@gagarin.work>]

On NixOS, repeating the default will make it show up in the
configuration twice.  We're now relying on option merging to do the right
thing.

On vanilla Linux, repeating was only necessary because not adding
`extra-` would override whatever was set otherwise.  This is generally
undesirable, which is why now we're using `extra-` and thus don't need
to repeat the defaults.

Signed-off-by: Valentin Gagarin <valentin@gagarin.work>
---
 Documentation/installation/binary-cache.adoc | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/Documentation/installation/binary-cache.adoc b/Documentation/installation/binary-cache.adoc
index a51e152..ec8d797 100644
--- a/Documentation/installation/binary-cache.adoc
+++ b/Documentation/installation/binary-cache.adoc
@@ -29,9 +29,10 @@ Add the following configuration to /etc/nixos/configuration.nix:
 { ... }:
 
 {
-  nix.settings.substituters = [ "https://cache.dataaturservice.se/spectrum/" ];
+  nix.settings.substituters = [
+    "https://cache.dataaturservice.se/spectrum/"
+  ];
   nix.settings.trusted-public-keys = [
-    "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
     "spectrum-os.org-2:foQk3r7t2VpRx92CaXb5ROyy/NBdRJQG2uX2XJMYZfU="
   ];
 }
@@ -49,8 +50,8 @@ Add the following configuration to /etc/nix/nix.conf:
 
 [source]
 ----
-substituters = https://cache.dataaturservice.se/spectrum/ https://cache.nixos.org/
-trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= spectrum-os.org-2:foQk3r7t2VpRx92CaXb5ROyy/NBdRJQG2uX2XJMYZfU=
+extra-substituters = https://cache.dataaturservice.se/spectrum/
+extra-trusted-public-keys = spectrum-os.org-2:foQk3r7t2VpRx92CaXb5ROyy/NBdRJQG2uX2XJMYZfU=
 ----
 
 Run `systemctl restart nix-daemon.service` after making any changes in the Nix
-- 
2.51.2