Tell Git how to check GitSetup config files

Add a .gitattributes line to match both "config.sample" and any config
file added by the containing project.

.gitattributes

@@ -3,5 +3,6 @@
 # Exclude from source archives files specific to Git work tree.
 *                export-ignore
 
+config*          eol=lf         whitespace=indent-with-non-tab
 tips             eol=lf         whitespace=indent-with-non-tab
 setup-*          eol=lf         whitespace=indent-with-non-tab