Enter tags separated by + from your Edit Sub Info page.
example: /s/space will have NASA+astronaut+cosmonaut+space station+Hubble+rocket+launch
looks like - https://i.imgur.com/Nqgngwb.png
Part two is add them to the sub search page so if anyone searches for one of the tags, your sub comes up
wish me luck :D
I will not abuse this at all with SDBH :D