Add def f($arg): syntax (fix #524)

docs/content/3.manual/manual.yml

@@ -1931,9 +1931,13 @@ sections:
           If you want the value-argument behaviour for defining simple
           functions, you can just use a variable:
 
-              def addvalue(f): f as $value | map(. + $value);
+              def addvalue(f): f as $f | map(. + $f);
 
-          With that definition, `addvalue(.foo)` will add the current
+          Or use the short-hand:
+
+              def addvalue($f): ...;
+
+          With either definition, `addvalue(.foo)` will add the current
           input's `.foo` field to each element of the array.
 
           Multiple definitions using the same function name are allowed.