Add .gitattributes to fix prettier behavior on Windows

Since prettier enforces LF line endings, it would forcefully convert Windows' CLRF linebreaks on every run, causing undesired changes for contributors using Windows.

This is taken from prettier's own `.gitattributes` file: https://github.com/prettier/prettier/blob/main/.gitattributes

Signed-off-by: nscuro <nscuro@protonmail.com>

.gitattributes

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