Replace "what can you do with nix?" section on front page

[proofconstruction]

The list does not fully represent what's going on on nix.dev and we don't have to advertise here, only describe what's going on.

[willbush]

I kinda like the promotional pitch for Nix's capabilities. Are you suggesting that site should focus more on the content of the site?

here's the list as the time I'm reading it (for context):

## What can you do with Nix?

The following list illustrates some of what can be achieved with the Nix ecosystem:

- {ref}`Reproducible development environments <ad-hoc-envs>`.
- Easy installation of software over URLs.
- Easy transfer of software environments between computers.
- {ref}`Declarative specification of Linux machines <deploying-nixos-using-terraform>`.
- {ref}`Reproducible integration testing using virtual machines <integration-testing-vms>`.
- Avoidance of version conflicts with already installed software.
- Installing software from source code.
- {ref}`Transparent build caching using binary caches <github-actions>`.
- Strong support for software auditability.
- {ref}`First-class cross compilation support <cross-compilation>`.
- Remote builds.
- Remote deployments.
- Atomic upgrades and rollbacks.

[fricklerhandwerk]

This is what we recently came up with for NGIpkgs together with @cleeyv:

This is what you can do with software from NGIpkgs:

• Run standalone programs locally with Nix
• Use libraries or tools to build software with Nixpkgs
• Deploy services to machines running NixOS

I'd like to have that on the front page, augmented with a few other killer features such as temporary environments, cross-compilation, and, naturally, doing anything that converts files to new files.