message: Document build badge for Gitlab CI
diff: @@ -142,8 +142,8 @@ license = "..."
  license-file = "..."
  # Optional specification of badges to be displayed on crates.io. The badges
  -# currently available are Travis CI and Appveyor latest build status, specified
  -# using the following parameters:
  +# currently available are Travis CI, Appveyor, and Gitlab latest build status,
  +# specified using the following parameters:
  [badges]
  # Travis CI: `repository` is required. `branch` is optional; default is `master`
  travis-ci = { repository = "...", branch = "master" }
  @@ -151,6 +151,8 @@ travis-ci = { repository = "...", branch = "master" }
  # `service` is optional; valid values are `github` (default), `bitbucket`, and
  # `gitlab`.
  appveyor = { repository = "...", branch = "master", service = "github" }
  +# Gitlab: `repository` is required. `branch` is optional; default is `master`
  +gitlab = { repository = "...", branch = "master" }
  ```
  The [crates.io](https://crates.io) registry will render the description, display
  