Add editorconfig (#13)

https://editorconfig.org/
https://github.com/rust-lang/rust/blob/master/.editorconfig

Author: philiptaron

.editorconfig

@@ -0,0 +1,15 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+charset = utf-8
+indent_style = space
+max_line_length = 100
+
+[*.rs]
+indent_size = 4
+
+[*.nix]
+indent_size = 2