Improve UX: better error message about debug buffer on startup errors

Minuscule things like these can make a huge difference if you are
a first time user of a new text editor.

src/main.cc

@@ -844,7 +844,7 @@ int run_server(StringView session, StringView server_init,
 
             if (startup_error and local_client)
                 local_client->print_status({
-                    "error during startup, see *debug* buffer for details",
+                    "error during startup, see `:buffer *debug*` for details",
                     local_client->context().faces()["Error"]
                 });