simplify description of nix-store --realise

according to team review

doc/manual/src/command-ref/nix-store.md

@@ -63,23 +63,13 @@ have an effect.
 ## Description
 
 Ensure that the given [store path]s are [valid].
-A store path is valid if all [store object]s in its [closure] can be read from the store.
 
-If a given path is a [store derivation], the command operates on the [output path]s of that derivation.
-
-If the paths are already valid, we are done immediately.
-Otherwise, the associated store objects in the paths' closure may be fetched from [substituter]s.
-
-Finally, if a store derivation was given as argument, the required store objects can be produced by running the associated build task.
-If no store derivation is given and no substitutes are available, realisation fails.
+If a given path refers to a [store derivation], the command additionally operates on the [output path]s of that derivation.
 
 [store path]: ../glossary.md#gloss-store-path
 [valid]: ../glossary.md#gloss-validity
-[store object]: ../glossary.md#gloss-store-object
-[closure]: ../glossary.md#gloss-closure
 [store derivation]: ../glossary.md#gloss-store-derivation
 [output path]: ../glossary.md#gloss-output-path
-[substituter]: ../glossary.md#gloss-substituter
 
 The output path of each derivation is printed on standard output. For
 non-derivations argument, the argument itself is printed.

doc/manual/src/glossary.md

@@ -165,7 +165,9 @@
     The [store derivation] that produced an [output path].
 
   - [validity]{#gloss-validity}\
-    A [store path] is *valid* if all of the following hold:
+    A store path is valid if all [store object]s in its [closure] can be read from the [store].
+
+    For a local store, this means:
     - The store path leads to an existing [store object] in that [store].
     - The store path is listed in the Nix database as being valid.
     - All paths in the store path's [closure] are valid.