Update Readme

[richardschwabe]

Readme should have instructions, an overview, etc. To get everyone started

Edited:

• [ ] Sysreptor References
• [ ] Documentation Links
• [ ] Badges
• [ ] Description
• [ ] Screencasts reptor in action

[richardschwabe]

I have updated the readme with a better structure. Of course, subject to change, but the overall design might be sufficient for now.

ToC created in VsCode with https://marketplace.visualstudio.com/items?itemName=yzhang.markdown-all-in-one

Command Palette (Ctrl-Shift-P) -> Markdown: Create Table of Contents

MIght want to set "markdown.extension.toc.updateOnSave": false, in config.