add .editorconfig

Editorconfig is supported by almost every IDE and (CLI) editor, either
as built-in or as plugin. It helps to set the right settings as you
type your text or code.

Author: phip1611

.editorconfig

@@ -0,0 +1,12 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+max_line_length = 80
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.{json,md,nix,toml,yml}]
+indent_style = space
+indent_size = 2