Remove `pycocotools` from `requirements.txt` (#582)

* Remove `pycocotools` from `requirements.txt`

git version is required for numpy > 1.18

* Remove `cython`, add pip install doc

docs/tutorials/INSTALL.md

@@ -59,6 +59,8 @@ COCO-API is needed for running. Installation is as follows:
     # Alternatively, if you do not have permissions or prefer
     # not to install the COCO API into global site-packages
     python setup.py install --user
+    # or with pip
+    pip install "git+https://github.com/cocodataset/cocoapi.git#subdirectory=PythonAPI"
 
 **Installation of COCO-API in windows:**
 

docs/tutorials/INSTALL_cn.md

@@ -55,6 +55,8 @@ python -c "import paddle; print(paddle.__version__)"
     make install
     # 若您没有权限或更倾向不安装至全局site-packages
     python setup.py install --user
+    # 或者使用pip安装
+    pip install "git+https://github.com/cocodataset/cocoapi.git#subdirectory=PythonAPI"
 
 **windows用户安装COCO-API方式：**
 

requirements.txt

@@ -3,8 +3,6 @@ docstring_parser @ http://github.com/willthefrog/docstring_parser/tarball/master
 typeguard ; python_version >= '3.4'
 tb-paddle
 tensorboard >= 1.15
-cython
-pycocotools
 opencv-python
 PyYAML
 shapely