add option to readme

README.md

@@ -419,6 +419,9 @@ flash_attention:  # require a100 for llama
 sdp_attention:
 # Landmark attention (only llama)
 landmark_attention:
+# xpos RoPE see https://github.com/kaiokendev/cutoff-len-is-context-len/blob/main/util/xpos_rope_llama_monkey_patch.py
+# llama only
+xpos_rope:
 
 # resume from a specific checkpoint dir
 resume_from_checkpoint: