chore: add .editorconfig (#536)

Co-authored-by: Adam Spiers <opencode@adamspiers.org>

.editorconfig

@@ -0,0 +1,9 @@
+root = true
+
+[*]
+charset = utf-8
+insert_final_newline = true
+end_of_line = lf
+indent_style = space
+indent_size = 2
+max_line_length = 80