Create .editorconfig (#889)

Co-authored-by: あく <alleteam@gmail.com>

.editorconfig

@@ -0,0 +1,13 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+charset = utf-8
+
+[*.{cpp,h,c,py,sh}]
+indent_style = space
+indent_size = 4
+
+[{Makefile,*.mk}]
+indent_size = tab