docs: document @arg.{positional,noDefaultName} (#185)

closes #184

Author: scarf005

readme.md

@@ -413,6 +413,11 @@ customize your usage:
 - `doc: String`: a documentation string used to provide additional information
   about the command
 
+- `noDefaultName: Boolean`: if `true` this arg (e.g `fooBar`) can only be called by its mangled name `--foo-bar` and not by the original name `--fooBar`. Defaults to `false`
+
+- `positional: Boolean`: if `true` this arg can be passed "positionally" without
+  the `--name` of the parameter being provided, e.g. `./mill example.hello hello 3 --bool`. Defaults to `false`
+
 - `hidden: Boolean`: if `true` this arg will not be included in the rendered help text.
 
 ## Customization