message: Recover doc for appveyor project_name
  First added in which failed
  to update the book and was replaced in
diff: @@ -200,7 +200,8 @@ license-file = "..."
  # Appveyor: `repository` is required. `branch` is optional; default is `master`
  # `service` is optional; valid values are `github` (default), `bitbucket`, and
  # `gitlab`; `id` is optional; you can specify the appveyor project id if you
  -# want to use that instead.
  +# want to use that instead. `project_name` is optional; use when the repository
  +# name differs from the appveyor project name.
  appveyor = { repository = "...", branch = "master", service = "github" }
  # Circle CI: `repository` is required. `branch` is optional; default is `master`
  