docs: add nix as an installation method

docs/installation.md

@@ -51,6 +51,19 @@ yay -S taskfile-git
 This installation method is community owned, but since it's `-git` version of
 the package, it's always latest available version based on the Git repository.
 
+
+#### **Nix**
+
+If you're on NixOS or have Nix installed
+you can install Task from [nixpkgs](https://github.com/NixOS/nixpkgs):
+
+```cmd
+nix-env -iA nixpkgs.go-task
+```
+
+This installation method is community owned. After a new release of Task, it
+may take some time until it's available in [nixpkgs](https://github.com/NixOS/nixpkgs).
+
 <!-- tabs:end -->
 
 ## Get The Binary

docs/releasing_task.md

@@ -31,6 +31,13 @@ of updating versions there by editing
 [this file](https://github.com/lukesampson/scoop-extras/blob/master/bucket/task.json).
 If you think its Task version is outdated, open an issue to let us know.
 
+# Nix
+
+Nix is a community owned installation method. Nix package maintainers usually take care
+of updating versions there by editing
+[this file](https://github.com/NixOS/nixpkgs/blob/nixos-unstable/pkgs/development/tools/go-task/default.nix#L34).
+If you think its Task version is outdated, open an issue to let us know.
+
 [goreleaser]: https://goreleaser.com/#continuous_integration
 [homebrewtap]: https://github.com/go-task/homebrew-tap
 [gotaskrb]: https://github.com/go-task/homebrew-tap/blob/master/Formula/go-task.rb