Simple ToDoList-App

[timunie]

What does the pull request do?

Scope of this PR:

• [ ] fix or update to an existing sample
• [X] add a new sample

Spoiler:

What is the current behavior?

The TodoList tutorial is kinda outdated and needs some updates and simplifications for beginners

Checklist

If this is a new Sample

• [x] Added a ReadMe-file
• [x] Updated the landing page
• [ ] Consider submitting a PR to https://github.com/AvaloniaUI/Documentation with a link to your sample in the related documentation page

In any case

• [ ] Spell-checking done
• [ ] Checked if all hyperlinks work
• [ ] Checked if all images are visible

Fixed issues