在Mac上使用brew命令安装东西，提示/usr/local/include is not writable的错误，在Stack Overflow很快找到解决办法：
Simple solution that worked for me:
click on your background to go to finder
click on go and go to folder /usr
right click on local and do get info
unlock the lock at the bottom
click + sign and add your user to the list and give read/write privileges
click on the gear sign at the
bottom and choose apply to enclosed items to recurse under that
directory and assign privileges too all directories beneath it.
