Inform users that search bar can be sorted

[DeniseSl22]

Since the search output in the DataNodes can now be sorted (see #90), I would like to inform users that they can sort the output.
Perhaps adding a line of text, saying sorting can be done by clicking on the column name?
And adding two arrows (one pointing up, one down) next to the name of the column would also help (but is maybe a bit more work).