Update README.md with new visuals/text

[bastianilso]

In preparation for the VR Workshop, it would be great with an update to the text/pictures of VR Eye tracking accuracy test in its current state in the README.md file. It should mainly cover:

• The motivation behind the accuracy test project.
• The intended use cases and audience.
• Bullet points with key features (pupil labs integration, assess accuracy across 9 different parts of the visual field in HMD, visualization of the gaze paths)
• Description of the connection to the R shiny application with a link to its git repository.
• A technical section on the data collection / what data is collected / explanation of what the columns means (which we already have).

[YoNeXia]

This issue was resolved with #27. So, I close it.