Introduce .editorconfig for ruby files

Many editors and IDEs will leverage an .editorconfig out of the box

This basic configuration for ruby files tells the editor to behave
per how rubocop is configured to handle whitespace

Author: Brian Butz

.editorconfig

@@ -0,0 +1,8 @@
+# EditorConfig is awesome: https://EditorConfig.org
+
+# top-most EditorConfig file
+root = true
+
+[*.rb]
+insert_final_newline = true
+trim_trailing_whitespace = true