Update .env.example with LETZAI_API_KEY

Author: mitchoz

.env.example

@@ -373,3 +373,7 @@ FUEL_WALLET_PRIVATE_KEY=
 # Tokenizer Settings
 TOKENIZER_MODEL=  # Specify the tokenizer model to be used.
 TOKENIZER_TYPE=   # Options: tiktoken (for OpenAI models) or auto (AutoTokenizer from Hugging Face for non-OpenAI models). Default: tiktoken.
+
+#LetzAI
+LETZAI_API_KEY= # LetzAI API Key
+LETZAI_MODELS= # list of Letzai models to add to each prompt, e.g.: "@modelname1, @modelname2"