Improve docs & Add JSON decode example (#121)

docs/sampling_params.md

@@ -4,13 +4,21 @@ This doc describes the sampling parameters of the SGLang Runtime.
 The `/generate` endpoint accepts the following arguments in the JSON format.
 
 ```python
+@dataclass
 class GenerateReqInput:
+    # The input prompt
     text: Union[List[str], str]
+    # The image input
     image_data: Optional[Union[List[str], str]] = None
+    # The sampling_params
     sampling_params: Union[List[Dict], Dict] = None
+    # The request id
     rid: Optional[Union[List[str], str]] = None
+    # Whether return logprobs of the prompts
     return_logprob: Optional[Union[List[bool], bool]] = None
+    # The start location of the prompt for return_logprob
     logprob_start_len: Optional[Union[List[int], int]] = None
+    # Whether to stream output
     stream: bool = False
 ```
 
@@ -84,3 +92,7 @@ for chunk in response.iter_lines(decode_unicode=False, delimiter=b"\0"):
         prev = len(output)
 print("")
 ```
+
+### Multi modal
+
+See [test_httpserver_llava.py](../test/srt/test_httpserver_llava.py).