[Doc] Improve api doc for perplexity (#31636)

- add param in api doc
- fix word spelling

---------

Co-authored-by: Chester Curme <[email protected]>

Author: ZhangShenao

libs/partners/perplexity/langchain_perplexity/chat_models.py

@@ -409,7 +409,7 @@ def with_structured_output(
         **kwargs: Any,
     ) -> Runnable[LanguageModelInput, _DictOrPydantic]:
         """Model wrapper that returns outputs formatted to match the given schema for Preplexity.
-        Currently, Preplexity only supports "json_schema" method for structured output
+        Currently, Perplexity only supports "json_schema" method for structured output
         as per their official documentation: https://docs.perplexity.ai/guides/structured-outputs
 
         Args:
@@ -433,6 +433,11 @@ def with_structured_output(
                 will be caught and returned as well. The final output is always a dict
                 with keys "raw", "parsed", and "parsing_error".
 
+            strict:
+                Unsupported: whether to enable strict schema adherence when generating
+                the output. This parameter is included for compatibility with other
+                chat models, but is currently ignored.
+
             kwargs: Additional keyword args aren't supported.
 
         Returns: