Add quick start & component info in readme

[jacobras]

This change includes:

• Quick start info (about CupertinoTheme and AdaptiveTheme)
• An overview of most of the (adaptive) components to the readme
• A link to my adaptive tutorial (I can remove it if you don't want it in the readme but I figured it makes sense as it offers a step-by-step introduction to using the library based on the well known KMP starter template)
• Info about using AdaptiveWidget for custom widgets
• Updates the Compose badge to 1.6.0-rc01 since that's the current version (RC2 is already out btw 😀)

I took some quick screenshots of some of the components to make the page a bit more visual and lead readers to what they're looking for. They're all exported at a maximum width of 300px.

You can check what this would look like on the repo in my fork: https://github.com/jacobras/compose-cupertino/tree/docs-improvement

[alexzhirkevich]

Can you please move it to the separate file Adaptive.md to the docs directory and left a link to it in a readme

[jacobras]

Can you please move it to the separate file Adaptive.md to the docs directory and left a link to it in a readme

Sure! Will update it today.

[jacobras]

Can you please move it to the separate file Adaptive.md to the docs directory and left a link to it in a readme

Sure! Will update it today.

PR updated @alexzhirkevich

[alexzhirkevich]

Thanks!