release to pypi on windows, linux and macos (#2644)

* release python

* fix twine upload only push tags, fix linux bdist_wheel so path error

* fix long_description_content_type

* remove log print

* set cibuildwheel version 1.6.3

* add pyproject.toml

* set release python only on push tag

* add ci build python 2.7

* remove python2.7; update readme.md

python/README.md

@@ -1,6 +1,21 @@
 # ncnn
 python wrapper of ncnn with [pybind11](https://github.com/pybind/pybind11), only support python3.x now.
 
+
+Install from pip
+==================
+
+ncnn is available as wheel packages for macOS, Windows and Linux distributions, you can install with pip:
+
+```
+python -m pip install -U pip
+python -m pip install -U ncnn
+```
+
+# Build from source
+
+If you want to build ncnn with some options not as default, or just like to build everything yourself, it is not difficult to build ncnn from source.
+
 ## Prerequisites
 
 **On Unix (Linux, OS X)**
@@ -8,6 +23,11 @@ python wrapper of ncnn with [pybind11](https://github.com/pybind/pybind11), only
 * A compiler with C++11 support
 * CMake >= 3.4
 
+**On Mac**
+
+* A compiler with C++11 support
+* CMake >= 3.4
+
 **On Windows**
 
 * Visual Studio 2015 or higher
@@ -79,6 +99,26 @@ import ncnn.model_zoo as model_zoo
 
 print(model_zoo.get_model_list())
 ```
+models now in model zoo are as list below:
+```bash
+mobilenet_yolov2
+mobilenetv2_yolov3
+yolov4_tiny
+yolov4
+yolov5s
+yolact
+mobilenet_ssd
+squeezenet_ssd
+mobilenetv2_ssdlite
+mobilenetv3_ssdlite
+squeezenet
+faster_rcnn
+peleenet_ssd
+retinaface
+rfcn
+shufflenetv2
+simplepose
+```
 all model in model zoo has example in ncnn/python/examples folder
 
 # Custom Layer