update readme

README.md

@@ -1,15 +1,63 @@
 # Nixin krops POC
-This is a proof of concept of using krops to deploy nixos configuration generated by nixin 
+This is a proof of concept of using krops to deploy nixos configurations generated by nixin  
+
+The configurations of each server are stored in a sub-directory of the config directory :  
+```
+├── config
+│   ├── server-01
+│   │   ├── configuration.nix
+│   │   └── hardware-configuration.nix
+│   └── server-02
+│       ├── configuration.nix
+│       └── hardware-configuration.nix
+```
+
+These configurations can reference shared modules stored in the modules directory  
+```
+├── modules
+│   └── nixin.nix
+```
+
+The file `nixpkgs.json` contains the revision of nixpkgs to use. See the tips section for how to update it  
+
+The file `krops.nix` is the main deployment configuration that ties everything up. If new servers are added to the config directory, they must also be added in this file.  
+
+The servers mush be accessible with ssh as `root` or as a user with passwordless sudo capability, as defined in `krops.nix`
+
+Secrets are stored in a sub directory of a separate git repository, managed with [passwordstore](https://www.passwordstore.org/)  
+This directory must available at ` ~/.password-store/nixin-password-store/krops`. (This is also defined in `krops.nix`)  
+When building the configuration on the server, the secrets files are decrypted and copied to the /var/srv/secret directory
+
+Sample `/var/src` on a server after configuration deployment : 
+```sh
+[root@arachnide:~]# ls -l /var/src
+total 20
+drwxr-xr-x  2 root root 4096 18 déc.  19:07 config
+drwxr-xr-x  2 root root 4096 18 déc.  21:39 modules
+lrwxrwxrwx  1 root root   24 19 déc.  10:28 nixos-config -> config/configuration.nix
+drwxr-xr-x 10 root root 4096 19 déc.  10:29 nixpkgs
+drwx------  2 root root 4096 19 déc.  10:30 secrets
+```
 
 ## Tips
-Deploy configuration of only one server :  
+
+The file `/var/src/.populate` needs to be created on target servers to be able to deploy a configuration to them. This is a protection to avoid deploying to a machine that is not meant to be managed with krops  
+
+Deploying configuration of only one server :  
 nix-build ./krops.nix -A arachnide && ./result
 
-Deploy configration of all servers :  
+Deploying configuration of all servers :  
 nix-build ./krops.nix -A all && ./result
 
-Update th revision of nixpkgs that is used :  
+Updating the nixpkgs revision that is used :  
+```sh
 nix-prefetch-git   --url https://github.com/NixOS/nixpkgs   --rev "refs/heads/nixos-24.11"   > nixpkgs.json
+```
+
+Rebuilding the system on the host itself :  
+```sh
+nixos-rebuild switch -I /var/src
+```
 
 ## References
 - krops : https://github.com/krebs/krops