doc: Add notes about revisions in Getting Started
@@ -45,6 +45,28 @@ and mainly, installation steps.
Fear not, look for your particular device on the <<devices/index.adoc#,devices list>>
page, will likely contain the necessary instructions.
+=== Using a known-good revision
+
+Things change, and sometimes things break. This is even more true with Mobile
+NixOS as the project depends on another moving target, NixOS.
+
+You can look at the
+link:https://hydra.nixos.org/job/mobile-nixos/unstable/tested/latest-finished#tabs-buildinputs[latest successful build's inputs]
+to see which _revisions_ were used for a successful build.
+
+You can then clone Nixpkgs somewhere, checkout that commit ID, and refer to it
+using `NIX_PATH`. The following is only an example of how one would do this.
+
+```
+$ cd ~/Projects/
+$ git clone https://github.com/NixOS/nixpkgs.git
+$ cd nixpkgs
+$ git checkout $revision
+$ cd ~/Projects/mobile-nixos/
+$ export NIX_PATH="nixpkgs=$HOME/Projects/nixpkgs"
+$ nix-build [...]
+```
+
=== Using a pre-built `system.img`
When bootstrapping yourself up, without an aarch64-linux system, it may be
