docs: Refer to the glossary with @docroot@ instead of ..

These unweildy relative paths probably predate the `@docroot@`
mechanism.

src/libcmd/command.cc

@@ -148,7 +148,7 @@ MixOperateOnOptions::MixOperateOnOptions()
 {
     addFlag({
         .longName = "derivation",
-        .description = "Operate on the [store derivation](../../glossary.md#gloss-store-derivation) rather than its outputs.",
+        .description = "Operate on the [store derivation](@docroot@/glossary.md#gloss-store-derivation) rather than its outputs.",
         .category = installablesCategory,
         .handler = {&operateOn, OperateOn::Derivation},
     });

src/nix/nix.md

@@ -229,7 +229,7 @@ operate are determined as follows:
   Note that a [store derivation] (given by its `.drv` file store path) doesn't have
   any attributes like `meta`, and thus this case doesn't apply to it.
 
-  [store derivation]: ../../glossary.md#gloss-store-derivation
+  [store derivation]: @docroot@/glossary.md#gloss-store-derivation
 
 * Otherwise, Nix will use all outputs of the derivation.
 

src/nix/path-info.md

@@ -70,7 +70,7 @@ R""(
 
 * Print the path of the [store derivation] produced by `nixpkgs#hello`:
 
-  [store derivation]: ../../glossary.md#gloss-store-derivation
+  [store derivation]: @docroot@/glossary.md#gloss-store-derivation
 
   ```console
   # nix path-info --derivation nixpkgs#hello

src/nix/store-copy-log.md

@@ -20,7 +20,7 @@ R""(
 
 * To copy the log for a specific [store derivation] via SSH:
 
-  [store derivation]: ../../glossary.md#gloss-store-derivation
+  [store derivation]: @docroot@/glossary.md#gloss-store-derivation
 
   ```console
   # nix store copy-log --to ssh-ng://machine /nix/store/ilgm50plpmcgjhcp33z6n4qbnpqfhxym-glibc-2.33-59.drv