Incorproate PR comments, correct erroneous description in clightning module, add electrs module, add electrs package, add electrs to nix-bitcoin.nix, add electrs to modules/nix-bitcoin.nix

modules/electrs.nix

@@ -0,0 +1,60 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.electrs;
+in {
+  options.services.electrs = {
+    enable = mkOption {
+      type = types.bool;
+      default = false;
+      description = ''
+        If enabled, the electrs service will be installed.
+      '';
+    };
+    dataDir = mkOption {
+      type = types.path;
+      default = "/var/lib/electrs";
+      description = "The data directory for electrs.";
+    };
+  };
+
+  config = mkIf cfg.enable {
+    users.users.electrs = {
+        description = "electrs User";
+        group = "electrs";
+        extraGroups = [ "bitcoinrpc" "keys" ];
+        home = cfg.dataDir;
+    };
+    users.groups.electrs = {
+      name = "electrs";
+    };   
+
+    systemd.services.electrs = {
+      description = "Run electrs";
+      wantedBy = [ "muli-user.target" ];
+      requires = [ "bitcoind.service" ];
+      after = [ "bitcoind.service" ];
+      # create shell script to start up electrs safely with password parameter
+      preStart = ''
+        mkdir -m 0770 -p ${cfg.dataDir}
+	chown 'electrs:electrs' ${cfg.dataDir}
+	echo "${pkgs.electrs}/bin/electrs -vvv --timestamp --db-dir ${cfg.dataDir} --daemon-dir /var/lib/bitcoind --cookie=${config.services.bitcoind.rpcuser}:$(cat /secrets/bitcoin-rpcpassword)" > /var/lib/electrs/startscript.sh
+	chown -R 'electrs:electrs' ${cfg.dataDir}
+	chmod u+x ${cfg.dataDir}/startscript.sh
+	'';	
+      serviceConfig = {
+	PermissionsStartOnly = "true";
+        ExecStart = "${pkgs.bash}/bin/bash ${cfg.dataDir}/startscript.sh";
+        User = "electrs";
+        Restart = "on-failure";
+        RestartSec = "10s";
+        PrivateTmp = "true";
+        ProtectSystem = "full";
+        NoNewPrivileges = "true";
+        PrivateDevices = "true";
+      };
+    };
+  };
+}