.editorconfig: add

This allows conveniently editing ebuilds and eclasses in editors which don't
have a specific ebuild mode like Emacs and Vim do.

For example, kde-apps/kate with kde-frameworks/ktexteditor[editorconfig] can
automatically read this file and adjust settings appropriately.

It's possible that going forward we may want to have pkgdev support custom
keys in this file for e.g. copyright year mangling too.

Signed-off-by: Sam James <sam@gentoo.org>

.editorconfig

@@ -0,0 +1,11 @@
+# https://editorconfig.org/
+root = true
+
+[*.{ebuild,eclass}]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+indent_style = tab
+indent_size = 4
+trim_trailing_whitespace = true
+#max_line_length = 80