Add EditorConfig

Signed-off-by: Tim Crawford <tcrawford@system76.com>

.editorconfig

@@ -0,0 +1,21 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.c]
+indent_size = 8
+indent_style = tab
+
+[{Makefile,Makefile.*,*.mk}]
+indent_size = 8
+indent_style = tab
+
+[*.md]
+indent_size = 2
+indent_style = space