chore: add editorconfig

Signed-off-by: Bart Jaskulski <bjaskulski@protonmail.com>

.editorconfig

+# This file is for unifying the coding style for different editors and IDEs
+# editorconfig.org
+
+# WordPress Coding Standards
+# https://make.wordpress.org/core/handbook/coding-standards/
+
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = tab
+indent_size = 4
+tab_width = 4