extract reference documentation on remote builds (#9526)

- move all reference documentation to the `builders` configuration setting
- reword documentation on machine specification, add examples
- disable showing the default value, as it rendered as `@/dummy/machines`, which is wrong
- highlight the examples
- link to the configuration docs for distributed builds
- builder -> build machine

Co-authored-by: Janik H <janik@aq0.de>

doc/manual/src/language/advanced-attributes.md

@@ -257,7 +257,7 @@ Derivations can declare some infrequently used optional attributes.
     of the environment (typically, a few hundred kilobyte).
 
   - [`preferLocalBuild`]{#adv-attr-preferLocalBuild}\
-    If this attribute is set to `true` and [distributed building is enabled](../advanced-topics/distributed-builds.md), then, if possible, the derivation will be built locally instead of being forwarded to a remote machine.
+    If this attribute is set to `true` and [distributed building is enabled](@docroot@/command-ref/conf-file.md#conf-builders), then, if possible, the derivation will be built locally instead of being forwarded to a remote machine.
     This is useful for derivations that are cheapest to build locally.
 
   - [`allowSubstitutes`]{#adv-attr-allowSubstitutes}\

doc/manual/src/language/derivations.md

@@ -36,7 +36,7 @@ It outputs an attribute set, and produces a [store derivation] as a side effect
   The system type on which the [`builder`](#attr-builder) executable is meant to be run.
 
   A necessary condition for Nix to build derivations locally is that the `system` attribute matches the current [`system` configuration option].
-  It can automatically [build on other platforms](../advanced-topics/distributed-builds.md) by forwarding build requests to other machines.
+  It can automatically [build on other platforms](@docroot@/language/derivations.md#attr-builder) by forwarding build requests to other machines.
 
   [`system` configuration option]: @docroot@/command-ref/conf-file.md#conf-system