Update README.md

Added info about `localVariablePrefix` which is no where else in the docs.

Author: kodonnell-heila

modules/swagger-codegen-maven-plugin/README.md

@@ -46,6 +46,7 @@ mvn clean compile
 - `apiPackage` - the package to use for generated api objects/classes
 - `invokerPackage` - the package to use for the generated invoker objects
 - `modelNamePrefix` and `modelNameSuffix` - Sets the pre- or suffix for model classes and enums
+- `localVariablePrefix` - adds a prefix for all generated local variables. Helps if your API has method names that conflict with local variable names.
 - `withXml` - enable XML annotations inside the generated models and API (only works with Java `language` and libraries that provide support for JSON and XML)
 - `configOptions` - a map of language-specific parameters (see below)
 - `configHelp` - dumps the configuration help for the specified library (generates no sources)