Add .gitattributes to force normalize EOLs if core.autocrlf didn't set

All text files force to LF.

To find special non-text files to add them filter you can use

    git ls-tree --name-only -r HEAD | xargs file -N | grep -v text

.gitattributes

@@ -0,0 +1,5 @@
+*       text eol=lf
+
+*.png   binary
+*.bin   binary
+*.elf   binary