/bin/sh: mysql_config: command not found

mac下pip install -r requirements.txt安装mysqlclient报错

```bash
Collecting mysqlclient==2.1.1 (from -r requirements.txt (line 17))
  Using cached mysqlclient-2.1.1.tar.gz (88 kB)
  Preparing metadata (setup.py) ... error
  error: subprocess-exited-with-error
  × python setup.py egg_info did not run successfully.
  │ exit code: <