editors/kate: add a sensible pkg-descr

editors/kate/pkg-descr

-KDE5 kate
+Kate is a Feature-Packed Text Editor
+
+Kate is packed with features that will make it easier for you to view and edit
+all your text files. Kate lets you to edit and view many files at the same
+time, both in tabs and split views, and comes with a wide variety of plugins,
+including an embedded terminal that lets you launch console commands directly
+from Kate, powerful search and replace plugins, and a preview plugin that can
+show you what your MD, HTML and even SVG will look like.
+
+WWW: https://kate-editor.org/