Update doc/manual/src/design/overview.md

Co-authored-by: Valentin Gagarin <[email protected]>

doc/manual/src/design/overview.md

@@ -5,7 +5,8 @@ Nix consists of layers that operate fairly independently.
 At the top is the *command line interface*, i.e. the argument parsing of the various Nix executables.
 
 Below that is the Nix *expression language*, in which packages and configurations are written.
-These are the layers which users interact with most.
+
+The command line and expression language are what users interact with most.
 
 Below that is the *store layer*, Nix' machinery to represent tracked files, dependencies, and fully elaborated build plans.
 It is also used for executing those build plans.