docs(nix): add documentation for devenv.sh

Signed-off-by: Matej Focko <[email protected]>

Author: mfocko

docs/deployment/nix.md

@@ -0,0 +1,59 @@
+---
+title: Nix & devenv support
+author: mfocko
+---
+
+# Nix & devenv support
+
+:::tip tl;dr
+
+Ideal for atomic linux distributions and macOS setup.
+
+There's one file (`devenv.nix`) containing everything that's needed to set up an
+environment for the project (`packit/deployment` in this case). All tools and
+deps are kept only for this project, i.e., they don't pollute the host system.
+
+Since Nix and devenv.sh support pinning, it is also possible to acquire
+a reproducible environment.
+
+direnv makes sure the development environment is set up upon entering the repo.
+
+:::
+
+## What is [Nix](https://nixos.org/)?
+
+From the homepage:
+
+> Nix is a tool that takes a unique approach to package management and system
+> configuration. Learn how to make reproducible, declarative and reliable systems.
+
+Basically you have global environment and smaller `nix-shell`s that are usually
+tied to git repos (or any other directory). You aim for as small base environment
+as possible, i.e., you don't want to keep all utilities / dependencies everywhere.
+
+One benefit, in comparison to containers, lies in the fact that the packages are
+defined by hash, name and version which allows them to be stored in a global
+location (usually `/nix`). Including packages in “environments” is done by
+adjusting `$PATH` (and related) variable.
+
+## What is [devenv.sh](https://devenv.sh/)?
+
+Builds on top of the _Nix_ and _nix-shell_ themselves. Is a bit more robust,
+cause it also allows specifying environment variables, defining tasks, services,
+and processes. For example it allows you to automatically spin up `nginx` or
+`postgres` server once you enter the repo.
+
+## Getting started
+
+Feel free to follow the [devenv.sh' “Getting Started”](https://devenv.sh/getting-started/).
+
+1. You need to have _Nix_ set up. (single-user / non-daemon setup is recommended
+   for users with SELinux enabled)
+2. Install the _devenv.sh_ itself.
+3. Have _direnv_ present (since it automatically loads the environment upon
+   entering the directory with _devenv.sh_).
+
+## Caveats
+
+Bitwarden CLI is currently broken on macOS, therefore it's not included in the
+devenv.sh' config.