Update lustre.md

doc.zih.tu-dresden.de/docs/data_lifecycle/lustre.md

@@ -98,18 +98,15 @@ setstripe           getstripe           setdirstripe        getdirstripe
 mkdir               rm_entry            pool_list           find
 check               osts                mdts                df
 [...]
-marie@login lfs help setstripe
-
 ```
 
 To get more information on a specific option, enter `help` followed by the option of interest:
 
 ```console
-marie@login lfs help setstripe
-setstripe: To create a file with specified striping/composite layout, or
-create/replace the default layout on an existing directory:
-usage: setstripe [--component-end|-E <comp_end>]
-[...]
+marie@login lfs help df
+df: report filesystem disk space usage or inodes usage of each MDS and all OSDs or a batch belonging to a specific pool.
+Usage: df [--inodes|-i] [--human-readable|-h] [--lazy|-l]
+          [--pool|-p <fsname>[.<pool>]] [path]
 ```
 
 More comprehensive documentation can be found in the man pages of lfs (`man lfs`).