[doc] add note for get_num_kv_splits in triton_backend (#6444)

python/sglang/srt/layers/attention/triton_backend.py

@@ -155,6 +155,9 @@ class TritonAttnBackend(AttentionBackend):
         seq_lens: torch.Tensor,
     ):
         num_token, num_seq = num_kv_splits.shape[0], seq_lens.shape[0]
+        # NOTE(alcanderian): Considering speculative_decodeing,
+        # num_kv_splits.shape[0] will be topk * real_num_token.
+        # And the real_num_token is num_seq in decoding phase.
         num_group = num_token // num_seq
 
         assert (