minor improvements

- README:
  - Add RTL

- examples/configuration.nix:
  - Fix comment

- btcpayserver.nix:
  - Use nbLib.addressWithPort
  - Embed optionalString like the other optionalStrings

- clboss.nix:
  - Improve description

- clightning.nix:
  - Option `extraConfig`: Add example, improve description.
  - Disable `log-timestamps`. Timestamps are already logged via journald.
  - Simplify `preStart` script

- electrs.nix:
  - Use `port` description wording like in other services.

modules/electrs.nix

@@ -12,7 +12,7 @@ let
     port = mkOption {
       type = types.port;
       default = 50001;
-      description = "RPC port.";
+      description = "Port to listen for RPC connections.";
     };
     dataDir = mkOption {
       type = types.path;