Suggested README improvements to clarify scope and help new contributors

[thomgit9]

Hi ,
I’ve found your repository very useful — thank you for making it open source.

While reading through the README, I took some time to improve the structure/clarity (mainly clarity, structure, content). This proposal updates [README.md](http://readme.md/) to provide a complete, structured overview of Boost.PFR, including badges, architecture, API summary, installation and testing instructions, links to examples and docs, license.

I didn’t want to push directly on your repo without asking — so I created a fork to showcase what I mean. You can review it here:
https://github.com/boostorg/pfr

If you think some of these changes make sense, I’d be happy to open a PR.

Let me know if you’d like me to propose this as a PR directly.

Thanks again for the project — it’s been very helpful.

Best,