add readthedocs (#208)

* add readthedocs configs

* update readme

* fix link

* update

* remove turbomind in api

* update

* fix comment and remove api

docs/zh_cn/switch_language.md

+## <a href='https://lmdeploy.readthedocs.io/en/latest/'>English</a>
+
+## <a href='https://lmdeploy.readthedocs.io/zh_CN/latest/'>简体中文</a>

requirements/docs.txt

+docutils==0.16.0
+m2r==0.2.1
+markdown>=3.4.0
+mistune==0.8.4
+myst-parser
+-e git+https://github.com/open-mmlab/pytorch_sphinx_theme.git#egg=pytorch_sphinx_theme
+recommonmark
+sphinx==4.0.2
+sphinx-copybutton
+sphinx_markdown_tables>=0.0.16
+sphinxcontrib-mermaid

requirements/readthedocs.txt

+mmengine
+torch
+transformers
+urllib3<2.0.0