Add a section for Git commit messages to the `.editorconfig` file, so
that editors with EditorConfig support will automatically format commit
messages according to the GNU style.
ChangeLog:
* .editorconfig (COMMIT_EDITMSG): New section.
insert_final_newline = true
tab_width = 8
+# Git commit messages
+[COMMIT_EDITMSG]
+indent_size = 8
+indent_style = tab
+max_line_length = 72
+trim_trailing_whitespace = true
+
# EditorConfig files
[.editorconfig]
charset = utf-8