Add readme

README.md

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+
+## Deploy
+Everything (all servers, all clients)
+
+```bash
+colmena apply switch
+```
+
+All Clients
+
+```bash
+colmena apply switch --on@client
+```
+
+Append `--on=HOSTNAME` or `--on=@TAG` to target specific hosts.
+
+
+### Building disk image
+You can build a ready to use disk image containing the whole system using the following command:
+
+```bash
+nix build .#images.<MACHINE_NAME>
+```
+
+
+## Secret management
+Secrets are encrypted using sops.
+Sops encrypts the secrets for all administrators and the target machines using the secret.
+
+### Prepare your system
+You must derive an age key from your SSH key:
+```bash
+mkdir -p ~/.config/sops/age
+read -s SSH_TO_AGE_PASSPHRASE
+export SSH_TO_AGE_PASSPHRASE
+ssh-to-age -private-key -i ~/.ssh/id_ed25519 > ~/.config/sops/age/keys.txt
+unset SSH_TO_AGE_PASSPHRASE
+```
+
+### Edit/show secrets
+Secrets are stored in `secrets.yaml` or in files in the `secrets` folder.
+To show or edit their content, use the `sops` command. I.e.:
+
+```
+sops machines/nfs/secrets.yaml
+```
+
+### Update encryption after fresh deployment
+The target machines ues the SSH host key of the target system to decryt the secrets required for that machine.
+Therefore the host keys spcified in `sops-config.nix` must be kept in sync with the actual host keys.
+These keys change after a fresh installation (a re-deployment, a changed disk, a lost filesystem).
+After the keys have been updates, the `contrib/updatekeys.sh` script must be executed.
+

contrib/updatekeys.sh

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+#!/usr/bin/env nix-shell
+#!nix-shell -i bash -p yq
+#shellcheck shell=bash
+
+if [[ ! -f ".sops.yaml" ]]; then
+    echo "Error: .sops.yaml file not found in $(pwd)"
+    echo "Please ensure you are running this script from the repository root directory."
+    exit 1
+fi
+
+# Schritt 1: Alle Regex aus der .sops.yaml-Datei extrahieren
+regex_list=$(yq -r '.creation_rules[].path_regex' .sops.yaml)
+
+# Schritt 2: Alle Dateien finden, die zu den Regex passen
+matching_files=()
+for regex in $regex_list; do
+  # Entferne eventuelle ^ und $ Zeichen, damit die Regex auch in find funktionieren
+  simplified_regex=$(echo "$regex" | sed 's/^\^//;s/\$$//')
+  found_files=$(find . -type f | grep -E "$simplified_regex")
+
+  # Füge die gefundenen Dateien zur Liste hinzu
+  for file in $found_files; do
+    matching_files+=("$file")
+  done
+done
+
+# Deduplizieren der Dateiliste mit mapfile
+mapfile -t unique_files < <(printf "%s\n" "${matching_files[@]}" | sort -u)
+
+# Schritt 3: sops updatekeys für jede Datei ausführen
+for file in "${unique_files[@]}"; do
+  echo "Updating keys for: $file"
+  sops updatekeys -y "$file"
+done
+
+echo "Finished updating keys."