JJ: Description from the destination commit:

setup_cmd: add --output-pubkey

JJ: Description from source commit:
use cmdliner

tools/offline.ml

@@ -1,13 +1,7 @@
 (* TODO
-   better cmd doc
-   change arguments: '_' -> '-'
-
    all management operations:
      /management/wire
      /management/wire/disable
-       -> how to build WireSetupMessage?
-          we need additional data to craft master_sig
-          maybe supposed to be found in the full payto-uri?
 
      /management/aml-officers
        -> /aml
@@ -85,25 +79,40 @@ let url =
   Arg.(required & opt (some string) None & info [ "url" ] ~doc)
 
 let setup_cmd =
-  let doc = "Generate offline master keys" in
+  let doc =
+    "Generate offline master keys, write private and public key to file"
+  in
   let output =
-    let doc = "output file" in
+    let doc = "private key output file" in
     Arg.(required & opt (some filepath) None & info [ "o"; "output" ] ~doc)
   in
+  let output_pubkey =
+    let doc =
+      "public key output file, default to --output parameter with a \".pub\" \
+       extension"
+    in
+    Arg.(value & opt (some filepath) None & info [ "output-pubkey" ] ~doc)
+  in
   Cmd.make (Cmd.info "setup" ~doc)
   @@
-  let+ output = output in
-  setup ~output
+  let+ output = output and+ output_pubkey = output_pubkey in
+  let output_pubkey = Option.value ~default:(output ^ ".pub") output_pubkey in
+  setup ~output ~output_pubkey
 
 let download_cmd =
-  let doc = "GET" in
+  let doc =
+    "use curl to send a GET request to --url, write response body to --output"
+  in
   Cmd.make (Cmd.info "download" ~doc)
   @@
   let+ output = output and+ url = url in
   download ~output ~url
 
 let upload_cmd =
-  let doc = "POST" in
+  let doc =
+    "use curl to send a POST request to --url, with request body set to \
+     --input file content"
+  in
   Cmd.make (Cmd.info "upload" ~doc)
   @@
   let+ input = input and+ url = url in