Fix #35: document nixpkgs version printing

Support self-hosted runners and always skip adding a channel

README.md

@@ -4,18 +4,18 @@
 
 Installs [Nix](https://nixos.org/nix/) on GitHub Actions for the supported platforms: Linux and macOS.
 
-By default it has no channels configured, you have to set `nix_path`
+By default it has no nixpkgs configured, you have to set `nix_path`
 by [picking a channel](https://status.nixos.org/)
 or [pin nixpkgs yourself](https://nix.dev/tutorials/towards-reproducibility-pinning-nixpkgs.html).
 
 # Features
 
 - Quick installation (~4s on Linux, ~20s on macOS)
-- Multi-User mode with sandboxing enabled on Linux
+- Multi-User installation (with sandboxing enabled only on Linux)
 - [Self-hosted github runner](https://docs.github.com/en/actions/hosting-your-own-runners/about-self-hosted-runners) support
-- Allows specifying Nix installation URL
-- Allows specifying extra Nix configration options
-- Allows specifying `$NIX_PATH` and channels
+- Allows specifying Nix installation URL via `install_url`
+- Allows specifying extra Nix configration options via `extra_nix_config`
+- Allows specifying `$NIX_PATH` and channels via `nix_path`
 
 ## Usage
 
@@ -41,7 +41,7 @@ See also [cachix-action](https://github.com/cachix/cachix-action) for
 simple binary cache setup to speed up your builds and share binaries
 with developers.
 
-# Usage with Flakes
+## Usage with Flakes
 
 ```
 name: "Test"
@@ -74,6 +74,17 @@ jobs:
 
 ---
 
+## FAQ
+
+### Is it possible to run NixOS tests / Qemu+KVM with GitHub Actions?
+
+[Currently GitHub Actions are not running on Azure instance types that support nested virtualization](https://github.com/actions/virtual-environments/issues/183#issuecomment-610723516).
+
+### How do I print nixpkgs version with the channel I have configured?
+
+
+```nix-instantiate --eval -E '(import <nixpkgs> {}).lib.version'```
+
 ## Hacking
 
 Install the dependencies