Fix setting python path in windows in INSTALL docs (#483)

docs/tutorials/INSTALL.md

@@ -86,14 +86,21 @@ Required python packages are specified in [requirements.txt](https://github.com/
 pip install -r requirements.txt
 ```
 
-**Make sure the tests pass:**
+**Specify the current Python path:**
 
+```shell
+# In Linux/Mac
+export PYTHONPATH=$PYTHONPATH:.
+# In windows
+set PYTHONPATH=%PYTHONPATH%;.
 ```
-export PYTHONPATH=`pwd`:$PYTHONPATH
+
+**Make sure the tests pass:**
+
+```shell
 python ppdet/modeling/tests/test_architectures.py
 ```
 
-
 ## Datasets
 
 PaddleDetection includes support for [COCO](http://cocodataset.org) and [Pascal VOC](http://host.robots.ox.ac.uk/pascal/VOC/) by default, please follow these instructions to set up the dataset.

docs/tutorials/INSTALL_cn.md

@@ -82,14 +82,21 @@ Python依赖库在[requirements.txt](https://github.com/PaddlePaddle/PaddleDetec
 pip install -r requirements.txt
 ```
 
+**指定当前Python路径：**
+
+```shell
+# 在Linux/Mac系统下运行:
+export PYTHONPATH=$PYTHONPATH:.
+# 在windows系统下运行:
+set PYTHONPATH=%PYTHONPATH%;.
+```
+
 **确认测试通过：**
 
 ```
-export PYTHONPATH=`pwd`:$PYTHONPATH
 python ppdet/modeling/tests/test_architectures.py
 ```
 
-
 ## 数据集