(maint) Update README.md

Author: GabrielNagy

README.md

@@ -26,7 +26,7 @@ To generate documentation locally, run the following command:
 
 ```
 bundle install
-bundle exec puppet strings generate ./lib/**/*.rb
+bundle exec puppet strings generate --format markdown --out REFERENCE.md
 ```
 
 This command will create a browsable \_index.html file in the doc directory. The references available here are all generated from YARD-style comments embedded in the code base. When any development happens on this module, the impacted documentation should also be updated.