WHile attempting to answer a related question here Install a customized app Espo CRM - Howto - NethServer Community
I found myself in a similar problem.
I tried to Upload a zipped file, only to find out that there was no unzip option on the UI.
My last resort was to Wget the file i need into the webserver folder, as visible from the webserver, volumes sections. worked well quite actually.
MAybe this might be an option you can look into using, i however faced some eprmissions issues, that i have been unable to fix with my current knowow, maybe you can work worund them.
I concur with you, the Documentations for webserver is abit Sparse