fixed README

Author: uechoco

README.md

@@ -40,7 +40,7 @@ These template variables are available.
   // DO NOT EDIT.; Code generated by "constconv -type=constant.Kind -template=const_kind.tmpl testdata/const_kind.go
   ```
 * `$.Extra`: Extra template data given by `-data` argument.
-  For example, if the argument `-data="package=dayofweek;typename=DayOfWeek"` given, the below template variables are available:
+  For example, if the argument `-data=package=dayofweek;typename=DayOfWeek` given, the below template variables are available:
   ```
   {{ $.Extra.package }}  // dayofweek
   {{ $.Extra.typename }} // DayOfWeek