Add documentation on ws_allocate's -g option

Because man pages for the ws_* tools are not available, please add information about the effects of all options, i. e. what ws_allocate -g does compared to only ws_allocate.

added Content New label

mentioned in commit 20b4e409

assigned to @mflehmig--tu-dresden.de

mentioned in merge request !806 (merged)

mentioned in commit ba11d84c

closed with merge request !806 (merged)

closed with commit 20b4e409