Document regexes for showing only attributes or datasets in new ADIOS2 schema (#1068)

* Document regexes for emulating bpls -A
* Reword introductory sentence

Co-authored-by: Axel Huebl <axel.huebl@plasma.ninja>

Author: franzpoeschel

docs/source/backends/adios2.rst

@@ -105,6 +105,15 @@ The new layout may be activated **for experimental purposes** in two ways:
 
 The ADIOS2 backend will automatically recognize the layout that has been used by a writer when reading a dataset.
 
+.. tip::
+
+   This schema does not use ADIOS2 attributes anymore, thus ``bpls -a`` and ``bpls -A`` attribute switches do not show openPMD attributes.
+   Their functionality can be emulated via regexes:
+
+   * Print datasets and attributes: Default behavior
+   * Print datasets only: ``bpls -e '.*/__data__$'``
+   * Print attributes only: ``bpls -e '^(.(?!/__data__$))*$'``
+
 Memory usage
 ------------