kcms/componentchooser: refine text on chooser overlay

This should be a bit more user-friendly.

| Before | After |
| ------ | ----- |
| ![Before](/uploads/ca534335619d1fc5a9a5ab8dc4262441/Before.jpeg) | ![image](/uploads/443b63ec4aee9efd817d803d80222d68/image.png) |

@teams/vdg @teams/usability