update readme

README.md

@@ -5,6 +5,21 @@ Nix setup for server
 ## Install
 
 ```bash
+# First time install
 curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix | sh -s -- install --determinate
+
+# Install / Update
 nix run home-manager -- switch --flake github:cupcakearmy/nix-cli#root -b bkp
 ```
+
+## Update
+
+This can be run on any machine. Just update and then just rerun on the targets
+
+```bash
+nix flake update
+```
+
+```
+
+```