correct nemoguardrails usage syntax

Author: zsimjee

docs/integrations/nemo_guardrails/guardrails_rails.md

@@ -16,11 +16,6 @@ from guardrails.hub import ToxicLanguage
 # Load a guardrails configuration from the specified path.
 config = RailsConfig.from_path("PATH/TO/CONFIG")
 rails = LLMRails(config)
-
-# Define a guardrails guard.
-guard = Guard().use(
-  ToxicLanguage()
-)
 ```
 
 Then, we have the guard validate the completions generated by the Rails application.
@@ -29,7 +24,7 @@ Then, we have the guard validate the completions generated by the Rails applicat
 from guardrails.integrations.nemoguardrails.nemoguardrails_guard import (
     NemoguardrailsGuard
 )
-railsguard = NemoguardrailsGuards(rails, guard)
+railsguard = NemoguardrailsGuards(rails).use(ToxicLanguage)
 
 result = railsguard(
   messages: [{