Is it OK to credit (CC BY 3.0) icons in my (GPLv2) Github project with a CREDITS.txt file?

I'm in the middle of uploading a project to github. My software uses some icons which are licensed: "Creative Commons (CC BY 3.0 US)"

Should i hardcode the credits in a..let's say "Help->About" dialog for the software or can I ship a CREDITS.txt file inside the source code tree on github. For example inside icons\ folder with credit to the authors and links?

Also can I use a MIT license for this case?