Add a .editorconfig, cribbed from zulip/zulip.

Author: alexmv

.editorconfig

@@ -0,0 +1,16 @@
+root = true
+
+[*]
+end_of_line = lf
+charset = utf-8
+indent_size = 4
+indent_style = space
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[[shell]]
+binary_next_line = true
+switch_case_indent = true
+
+[*.{yaml,yml}]
+indent_size = 2