Fix estd reference

Author: rolandreichweinbmw

libs/bsw/util/doc/user/index.rst

@@ -20,6 +20,7 @@ Submodules
 -  :ref:`util::assert <util_assert>`- assert
 -  :ref:`util::command <util_command>` - command framework
 -  :ref:`util::crc <util_crc>` - cyclic redundancy check
+-  :ref:`util::estd <util_estd>` - extensions for ETL
 -  :ref:`util::format <util_format>` - `printf`-like string formatting
 -  :ref:`util::defere <util_defer>` - deferred function execution
 -  :ref:`util::logger <util_logger>` - logging functionality
@@ -34,6 +35,7 @@ Submodules
    assert <assert>
    command <command>
    crc <crc>
+   estd <estd>
    format <format>
    defer <defer>
    logger <logger>