Revert unnecesary changes in doc/ci/variables/README.md

doc/ci/variables/README.md

@@ -37,7 +37,7 @@ future GitLab releases.**
 |-------------------------------- |--------|--------|-------------|
 | **CI**                          | all    | 0.4    | Mark that job is executed in CI environment |
 | **CI_COMMIT_REF_NAME**          | 9.0    | all    | The branch or tag name for which project is built |
-| **CI_COMMIT_REF_SLUG**          | 9.0    | all    | `$CI_COMMIT_REF_NAME` lowercased, shortened to 63 bytes, and with everything except `0-9` and `a-z` replaced with `-`. Use in URLs and domain names. |
+| **CI_COMMIT_REF_SLUG**          | 9.0    | all    | `$CI_COMMIT_REF_NAME` lowercased, shortened to 63 bytes, and with everything except `0-9` and `a-z` replaced with `-`. No leading / trailing `-`. Use in URLs, host names and domain names. |
 | **CI_COMMIT_SHA**               | 9.0    | all    | The commit revision for which project is built |
 | **CI_COMMIT_TAG**               | 9.0    | 0.5    | The commit tag name. Present only when building tags. |
 | **CI_DEBUG_TRACE**              | all    | 1.7    | Whether [debug tracing](#debug-tracing) is enabled |