Summary:
* scope examples with ``` and code type
* serviceByDesktopName is the correct method
* drop 0 parameter from createInstance call (nullptr is default arg)
* drop NO_MODULE from find_package(KF5TextEditor), not really needed,
  more simple example

Reviewers: #kate, cullmann

Reviewed By: #kate, cullmann

Subscribers: kwrite-devel, kde-frameworks-devel

Tags: #kate, #frameworks

Differential Revision: https://phabricator.kde.org/D27512