shorten system setting description

src/libstore/globals.hh

@@ -194,12 +194,12 @@ public:
         this, SYSTEM, "system",
         R"(
           The system type of the current Nix installation.
-
-          Nix can only build [derivations](@docroot@/language/derivations.md) whose `system` attribute equals the value specified here.
-          In general, it never makes sense to modify this value, since you can use it to ‘lie’ about the system you are building on (e.g., perform a macOS build on a Linux machine; the result would obviously be wrong).
-          It only makes sense if the Nix binaries can run on multiple platforms, e.g., ‘universal binaries’ that run on `x86_64-linux` and `i686-linux`.
+          Nix will only build [derivations](@docroot@/language/derivations.md) whose `system` attribute equals the value specified here.
 
           The default value is set when Nix itself is compiled for the system it will run on.
+          In general, it never makes sense to modify this value.
+          While you can force Nix to run a Darwin-specific `builder` executable on a Linux machine, the result would obviously be wrong.
+
           The following system types are widely used, as Nix is actively supported on these platforms:
 
           - `x86_64-linux`
@@ -207,35 +207,9 @@ public:
           - `i686-linux`
           - `aarch64-linux`
           - `aarch64-darwin`
+          - `armv6l-linux`
+          - `armv7l-linux`
 
-          The concrete value is based on the output of [`config.guess`](https://git.savannah.gnu.org/cgit/config.git/tree/config.guess):
-
-          ```
-          <cpu>-<vendor>-<os>[<version>][-<abi>]
-          ```
-
-          When Nix is built such that `./configure` is passed any of the `--host`, `--build`, `--target` options, the value is based on the output of [`config.sub`](https://git.savannah.gnu.org/cgit/config.git/tree/config.sub):
-
-          ```
-          <cpu>-<vendor>[-<kernel>]-<os>
-          ```
-
-          Nix only uses the CPU and OS identifiers:
-
-          ```
-          <cpu>-<os>[-<abi>]
-          ```
-
-          For historic reasons and backwards-compatibility, some CPU and OS identifiers are transformed as follows:
-
-          | `config.guess`             | Nix                 |
-          |----------------------------|---------------------|
-          | `amd64`                    | `x86_64`            |
-          | `i*86`                     | `i686`              |
-          | `arm6`                     | `arm6l`             |
-          | `arm7`                     | `arm7l`             |
-          | `linux-gnu*`               | `linux`             |
-          | `linux-musl*`              | `linux`             |
         )"};
 
     Setting<time_t> maxSilentTime{