Clarify that project URL could be HTTP or HTTPS

doc/ci/variables/README.md

@@ -92,7 +92,7 @@ future GitLab releases.**
 | **CI_PROJECT_NAMESPACE**                  | 8.10   | 0.5    | The project namespace (username or groupname) that is currently being built |
 | **CI_PROJECT_PATH**                       | 8.10   | 0.5    | The namespace with project name |
 | **CI_PROJECT_PATH_SLUG**                  | 9.3    | all    | `$CI_PROJECT_PATH` lowercased and with everything except `0-9` and `a-z` replaced with `-`. Use in URLs and domain names. |
-| **CI_PROJECT_URL**                        | 8.10   | 0.5    | The HTTP address to access project |
+| **CI_PROJECT_URL**                        | 8.10   | 0.5    | The HTTP(S) address to access project |
 | **CI_PROJECT_VISIBILITY**                 | 10.3   | all    | The project visibility (internal, private, public) |
 | **CI_REGISTRY**                           | 8.10   | 0.5    | If the Container Registry is enabled it returns the address of GitLab's Container Registry |
 | **CI_REGISTRY_IMAGE**                     | 8.10   | 0.5    | If the Container Registry is enabled for the project it returns the address of the registry tied to the specific project |