Revise `Explore by topic` section on the docs homepage and make sure we feature the most important topics

[pavlenex]

The Explore by topic page should be revised and we should discuss which articles we'd like to feature and in what order.

[pavlenex]

• What is BTCPay and how it works?
• Getting Started
• FAQ

....

[Bas02]

Yoo

What if we do the top three (left to right) about BTCPay Server the what/why/how.

What is BTCPay Server? https://docs.btcpayserver.org/Guide/

Why BTCPay Server? https://docs.btcpayserver.org/UseCase/

How to deploy BTCPay Server? https://docs.btcpayserver.org/TryItOut/

Then the second row (left to right) be about the main function/features that one would set up.

Wallet Setup https://docs.btcpayserver.org/WalletSetup/

Lightning Network setup https://docs.btcpayserver.org/LightningNetwork/

How to setup POS https://docs.btcpayserver.org/Apps/#point-of-sale-app

And have the bottom row left for Api docs/faq /contributing;

Greenfield Api https://docs.btcpayserver.org/API/Greenfield/v1/

FAQ https://docs.btcpayserver.org/FAQ/

Contribute https://docs.btcpayserver.org/Contribute/

[pavlenex]

Done ✅ in https://github.com/btcpayserver/btcpayserver-doc/pull/1166