Add editorconfig

Summary:
Defaults taken from kde coding style.
This file enables a minimum style guide to be enforced across editors,
like line endings, character encoding, tabs vs spaces, indent size
and some more.
https://editorconfig.org/

Reviewers: hindenburg, tcanabrava, gszymaszek

Reviewed By: hindenburg, tcanabrava, gszymaszek

Subscribers: Omar, gszymaszek, dhaumann, konsole-devel

Tags: #konsole

Differential Revision: https://phabricator.kde.org/D15383

.editorconfig

@@ -0,0 +1,14 @@
+# https://editorconfig.org
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+indent_size = 4
+indent_style = space
+insert_final_newline = true
+max_line_length = 100
+trim_trailing_whitespace = true
+
+[*.md]
+trim_trailing_whitespace = false