How to specify additional files/directories to ignore for Silver Searcher (Ag)?

Workflow
1

I use the thoughtbot/dotfiles as a basis for managing dotfiles. One thing I don’t know how to do is to tell Silver Searcher (Ag) additional files/directories to ignore when searching. In the thoughtbot/dotfiles, the agignore file has:

.git/
tags
/bower_components
/log
...

Any idea how I can use a custom file like agignore.local to specify additional files/directories to ignore? Or maybe some other approach?
Thanks!

2

I don’t ag supports an extention. Unfortunately you’ll like need to copy the file over into a personal set of dotfiles and include that.