Contributing: add details for UI changes

[maxwxyz]

Adding a mandatory presentation for UI changing pull requests.

If a PR changes the user interface (UI), the body of the text MUST include a presentation of these UI changes, preferably with screenshots of the previous and revised state.

[FEA-eng]

I guess that screenshots are needed only for bigger UI changes like toolbar modifications and task panel overhauls? If I only change some text in the task panel or update an icon then the screenshots aren't necessary as the commits themselves should be sufficient?

[maxwxyz]

I think also tooltips should be presented in the body, it must not be a screenshot but it can be text only. Otherwise you have to go through the files and compare.
For icon changes I'd still suggest screenshots as e.g. on the mobile GitHub app, .svg are not displayed as images but the code only. I'm not capable of drawing the icon in my head by looking at the .svg code 😉

[FEA-eng]

Ok, makes sense and I’ll follow these rules.

I can see the icons on mobile but I’m using a browser, not GitHub app (I didn’t know there is one).