.gitconfig file is stored into your home folder, for example C:\Users\bartsimpson or /home/bartsimpson.
In general, is not necessary to edit this file. You can find more information about how to edit git configuration in git-config Manual Page. In general Git GUI editors, have tools to help you on this.
Only an advertisement, in order to avoid line endings conversion problems we recommend to keep is as is by default:
[core]
autocrlf = false
safecrlf = false
The property safecrlf = false is to avoid warning errors converting line endings in the files that we choose to convert automatically.
See more information in dealing with line endings
Some text extracted from http://git-scm.com/docs/git-config (CC BY SA 3.0)