RPM Spec: add MIME type

Summary: Obtained from shared-mime-info: https://www.freedesktop.org/wiki/Software/shared-mime-info/

Reviewers: Framework: Syntax Highlighting, vkrause

Reviewed By: Framework: Syntax Highlighting, vkrause

Subscribers: kwrite-devel, bcooksley, kde-frameworks-devel

Tags: Frameworks, Kate

Differential Revision: https://phabricator.kde.org/D14020