add FAQ for installing

docs/FAQ.md

@@ -0,0 +1,20 @@
+## 无法自动安装PyUnitReport依赖库
+
+如果安装过程中出现如下报错：
+
+```text
+Downloading/unpacking PyUnitReport (from ApiTestEngine)
+  Could not find any downloads that satisfy the requirement PyUnitReport (from ApiTestEngine)
+```
+
+那么需要先手动安装`PyUnitReport`，安装方式如下：
+
+```bash
+$ pip install git+https://github.com/debugtalk/PyUnitReport.git#egg=PyUnitReport
+```
+
+然后再重新安装`ApiTestEngine`即可。
+
+```bash
+$ pip install git+https://github.com/debugtalk/ApiTestEngine.git#egg=ApiTestEngine
+```