doc: Add example of inherit in a let expression

doc/manual/src/language/constructs.md

@@ -132,6 +132,32 @@ a = src-set.a; b = src-set.b; c = src-set.c;
 when used while defining local variables in a let-expression or while
 defining a set.
 
+in a let expression, inherit can be used to selectively bring specific attributes of a set into scope. For example
+
+
+```nix
+let
+  x = { a = 1; b = 2; };
+  inherit (builtins) attrNames;
+in
+{
+  names = attrNames x;
+}
+```
+
+is equivalent to
+
+```nix
+let
+  x = { a = 1; b = 2; };
+in
+{
+  names = builtins.attrNames x;
+}
+```
+
+both resolve to `{ names = [ "a" "b" ]; }`.
+
 ## Functions
 
 Functions have the following form: