feat(editorconfig): Add a .editorconfig file to the project

Modern editors read this file and use it to enforce formatting
consistency in files for a project.

See: https://editorconfig.org/

Settings were made accoring to what is written in the CONTRIBUTING.md
file.

.editorconfig

@@ -0,0 +1,7 @@
+# See: https://editorconfig.org/
+
+root = true
+
+[*]
+indent_style = space
+indent_size = 4