Update lookup-path.md

Updated this entry with 2 sentence taken from the `nix.dev` tutorial's [lookup paths](https://nix.dev/tutorials/nix-language#lookup-paths) section as that resource makes it way easier to understand this concept.

Also added "_file system_" in front of "_path value_" because I found it an important clarification as "_path_" is an overloaded term.

doc/manual/src/language/constructs/lookup-path.md

@@ -4,14 +4,16 @@
 >
 > *lookup-path* = `<` *identifier* [ `/` *identifier* ]... `>`
 
-A lookup path is an identifier with an optional path suffix that resolves to a [path value](@docroot@/language/types.md#type-path) if the identifier matches a search path entry.
+A lookup path is an identifier with an optional path suffix that resolves to a file system [path value](@docroot@/language/types.md#type-path) if the identifier matches a search path entry.
 
 The value of a lookup path is determined by [`builtins.nixPath`](@docroot@/language/builtins.md#builtins-nixPath).
 
 See [`builtins.findFile`](@docroot@/language/builtins.md#builtins-findFile) for details on lookup path resolution.
 
 > **Example**
 >
+> Generally, `<nixpkgs>` points to the file system path of some revision of [Nixpkgs](https://nix.dev/reference/glossary#term-Nixpkgs).
+> 
 > ```nix
 > <nixpkgs>
 >```
@@ -20,6 +22,8 @@ See [`builtins.findFile`](@docroot@/language/builtins.md#builtins-findFile) for
 
 > **Example**
 >
+> `<nixpkgs/lib>` points to the subdirectory `nixos` of the file system path `<nixpkgs>` points to:
+> 
 > ```nix
 > <nixpkgs/nixos>
 >```