README.md in fluent-plugin-geoip-0.7.0 vs README.md in fluent-plugin-geoip-0.8.0

@@ -26,9 +26,11 @@
 $ sudo apt-get install libmaxminddb-dev
 
 # for OS X
 $ brew install geoip
 $ brew install libmaxminddb
+$ bundle config build.geoip-c --with-geoip-dir=/usr/local/include/
+$ bundle config build.geoip2_c --with-opt-include=/usr/local/include/
 ```
 
 ## Installation
 
 install with `gem` or td-agent provided command as: