message: docs(rpc): fix rpc doc for Topic
diff: @@ -84,6 +84,9 @@ def write_method_signature(file, method_name, vars):
  file.write(' * `{}`: {}\n'.format(var.name, var.ty))
  else:
  file.write('* `{}()`\n'.format(method_name))
  + if method_name == 'subscribe':
  + file.write('* result: `string`\n')
  + else:
  file.write('* result: {}\n'.format(vars[-1].ty))
  @@ -674,7 +677,7 @@ class RPCDoc(object):
  if 'ckb_types/packed' in path:
  return
  - if path.split('/')[-1] in ['type.Result.html', 'struct.Subscriber.html', 'enum.SubscriptionId.html']:
  + if path.split('/')[-1] in ['type.Result.html', 'struct.Subscriber.html', 'enum.SubscriptionId.html', 'enum.Topic.html']:
  return
  with open(path) as file:
  