Added pipelines directory to index

Author: jdesanto

docs/source/index.rst

@@ -56,6 +56,7 @@ Oracle Accelerated Data Science SDK (ADS)
    user_guide/big_data_service/index
    user_guide/jobs/index
    user_guide/logs/logs
+   user_guide/pipeline/index
    user_guide/secrets/index
    user_guide/model_version_set/index