doc: add Nix documentation

Co-authored-by: Markus Neteler <[email protected]>

doc/NIX.md

@@ -0,0 +1,103 @@
+# How to use Nix
+
+## What is Nix
+
+[Nix](https://nixos.org/) is a powerful package manager and system configuration
+tool that aims to make software deployment fully reproducible.
+
+## Nix installation
+
+- Install Nix
+  [(learn more about this installer)](https://zero-to-nix.com/start/install)
+
+  ```bash
+  curl --proto '=https' --tlsv1.2 -sSf \
+     -L https://install.determinate.systems/nix \
+     | sh -s -- install
+  ```
+
+## Create GRASS GIS development environment
+
+Nix provides a development environment containing all required dependencies.
+
+- Launch development environment
+
+  ```bash
+  nix develop
+  ```
+
+- Optionally, use [direnv](https://direnv.net) to activate environment
+  automatically when entering the source code directory
+
+  ```bash
+  echo "use flake" > .envrc
+  direnv allow
+  ```
+
+## Launch GRASS GIS directly from the source code
+
+Nix allows to run a program directly from git source code repository using
+following command:
+
+```bash
+nix run \
+  github:<OWNER>/<REPO>/<REVISION|BRANCH|TAG>#<PACKAGE-NAME> -- <PROGRAM-ARGUMENTS>
+```
+
+- Launch latest version of GRASS from `main` branch
+
+  ```bash
+  nix run github:OSGeo/grass#grass
+  ```
+
+- Launch GRASS from specific Git revision, branch or tag
+
+  ```bash
+  nix run github:OSGeo/grass/<REVISION|BRANCH|TAG>#grass
+  ```
+
+- Launch GRASS from pull request
+
+  ```bash
+  nix run github:<PR-OWNER>/grass/<PR-BRANCH>#grass
+  ```
+
+## Install GRASS GIS directly from the source code
+
+To install a program permanently, use following command:
+
+```bash
+nix profile install \
+  github:<OWNER>/<REPO>/<REVISION|TAG|BRANCH>#<PACKAGE-NAME> -- <PROGRAM-ARGUMENTS>
+```
+
+- Install latest version of GRASS from `main` branch
+
+  ```bash
+  nix profile install github:OSGeo/grass#grass
+  ```
+
+- Install GRASS from specific Git revision, branch or tag
+
+  ```bash
+  nix profile install github:OSGeo/grass/<REVISION|BRANCH|TAG>#grass
+  ```
+
+## Uninstall GRASS GIS
+
+- List installed programs
+
+  ```bash
+  nix profile list
+  ```
+
+- Uninstall a program
+
+  ```bash
+  nix profile remove <INDEX-NUMBER>
+  ```
+
+## Nix documentation
+
+- [nix.dev](https://nix.dev)
+- [Zero to Nix](https://zero-to-nix.com)