* langchain readthedocs update * solve langchain.llms.transformersllm issues * langchain.embeddings.transformersembeddings/transfortmersllms issues * update docs for get_num_tokens * add low_bit api doc * add optimizer model api doc * update rst index * fix coomments style * update docs following the comments * update api doc
* change to bigdlllm * update
* api doc initial * update desc