Reorder inferred `--parent` flag bug or instructions are incorrect

[kylebjordahl]

When performing a reorder, the instructions seem to imply that the --parent flag is optional for all but the first stack-branch entry, implying that the following should work, but in fact it results in an error: error: invalid stack-branch command: --parent=<branch> or --trunk=<branch> must be specified when creating the first branch

Seems like either the instructions are incorrect, or there is a bug here.

stack-branch kb/branch-1 --trunk main@0535d346e78e1236f63ea46349ff87fe8c8328f3
pick f51d843  # thing 1

stack-branch kb/branch-2 
pick 7084b61  # thing 2

# Instructions:
#
# Commands:
# sb, stack-branch <branch-name> [--parent <parent-branch-name> | --trunk <trunk-branch-name>]
#         Create a new branch as part of a stack. If parent is not specified,
#         the previous branch in the stack is used (if any). If trunk is
#         specified, the branch is rooted from the given branch.
#         trunk-branch-name can be either a branch name or a branch name with a
#         commit ID in the format "<branch-name>@<commit-id>".
# p, pick <commit-id>
#         Pick a commit to be included in the stack. Only valid after a
#         stack-branch command.