chore: add .editorconfig (#855)

This adds a simple `.editorconfig` file to the root of the repository so
that different editors/IDEs may pick up the settings. This makes it
easier to have consistent formatting while editing, not just after
running `cargo fmt`. See [here](https://editorconfig.org) for more details.

Co-authored-by: AlphaKeks <alphakeks@dawn.sh>

.editorconfig

@@ -0,0 +1,16 @@
+# EditorConfig is awesome: https://EditorConfig.org
+
+# top-most EditorConfig file
+root = true
+
+# Unix-style newlines with a newline ending every file
+[*]
+end_of_line = lf
+insert_final_newline = true
+
+# Indentation settings matching the default rustfmt config
+[*.rs]
+charset = utf-8
+indent_style = space
+indent_size = 4
+