formatting: Create a .editorconfig to nudge more consistent formatting

I checked all hand written text file extensions in use and most of them
already use 4 space indent majorly. The only exceptions are *.sh, which
is a wild chaos were any arbitrary decision will do, and *.nix where two
space indenting is prevalent in the Nix community (i.e., Nixpkgs).

See https://editorconfig.org/ for the specification and the goals of
`.editorconfig` files.

Author: ibbem

.editorconfig

@@ -0,0 +1,14 @@
+root = true
+
+# We let Git handle end_of_line such that this setting is effectively platform
+# dependent but still normalized in the Git store. See .gitattributes
+
+[*]
+charset = utf-8
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = space
+indent_size = 4
+
+[*.nix]
+indent_size = 2