Add .gitattributes to ensure line endings are normalized

This attribute enables and controls end-of-line normalization. When a text file is normalized, its line endings are converted to LF in the repository.

Source:
https://www.kernel.org/pub/software/scm/git/docs/gitattributes.html#_tt_text_tt

.gitattributes

@@ -0,0 +1 @@
+* text=auto