docs: update readme (#43)

Author: beeb

README.md

@@ -74,7 +74,8 @@ Options:
       --constructor        Enforce that constructors have NatSpec
       --struct-params      Enforce that structs have `@param` for each member
       --enum-params        Enforce that enums have `@param` for each variant
-  -f, --enforce <TYPE>     Enforce NatSpec (@dev, @notice) on items even if they don't have params/returns/members (can be used more than once)
+  -f, --enforce <TYPE>     Enforce NatSpec on items even if they don't have params/returns/members (can be used more than once)
+                           [possible values: constructor, enum, error, event, function, modifier, struct, variable]
       --json               Output diagnostics in JSON format
       --compact            Compact output
       --sort               Sort the results by file path