[triton] added copyright information for flash attention (#2835)

* [triton] added copyright information for flash attention

* polish code

LICENSE

@@ -201,9 +201,10 @@ Copyright 2021- HPC-AI Technology Inc. All rights reserved.
    See the License for the specific language governing permissions and
    limitations under the License.
 
-## Some of colossal-ai's code is derived from Alpa, which is subject to the following copyright notice:
+   ## Some of colossal-ai's code is derived from others projects, which is subject to the following copyright notice:
+
+   Copyright 2021 The Alpa team.
 
-Copyright 2021 The Alpa team.
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at
@@ -215,3 +216,16 @@ Copyright 2021 The Alpa team.
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
+
+   -------------------------------------------------
+
+   Copyright 2018-2020 Philippe Tillet
+   Copyright 2020-2022 OpenAI
+
+   Permission is hereby granted, free of charge, to any person obtaining
+   a copy of this software and associated documentation files
+   (the "Software"), to deal in the Software without restriction,
+   including without limitation the rights to use, copy, modify, merge,
+   publish, distribute, sublicense, and/or sell copies of the Software,
+   and to permit persons to whom the Software is furnished to do so,
+   subject to the following conditions:

colossalai/kernel/cuda_native/flash_attention.py

 """
-Fused Attention
-===============
-This is a Triton implementation of the Flash Attention algorithm
-(see: Dao et al., https://arxiv.org/pdf/2205.14135v2.pdf; Rabe and Staats https://arxiv.org/pdf/2112.05682v2.pdf; Triton https://github.com/openai/triton)
+The triton-based flash attention implementation is copied from the OpenAI/triton repository
+
+You can find the repository in Triton https://github.com/openai/triton
+You can find the source file in https://github.com/openai/triton/blob/main/python/tutorials/06-fused-attention.py
+
+Reference:
+1. Dao et al., https://arxiv.org/pdf/2205.14135v2.pdf
+2. Rabe and Staats https://arxiv.org/pdf/2112.05682v2.pdf
 """
 
 import math
@@ -56,7 +60,8 @@ except ImportError:
     print('please install xformers from https://github.com/facebookresearch/xformers')
 
 if HAS_TRITON:
-
+    # the following functions are adapted from the OpenAI Triton tutorial
+    # https://github.com/openai/triton/blob/main/python/tutorials/06-fused-attention.py
     @triton.jit
     def _fwd_kernel(
         Q,