These warnings should all be fixed now that ST2U is available as a proper UMP package. Thank-you for your patience. This has been a long time coming.
1 year ago (+1)
It's another installation method for a unity package. Instead of dropping a folder into the packages folder locally, it can be downloaded straight from the unity package manager, even checking for and downloading updates with an easy update button. You can request the OpenUPM devs to have your repo be recognized and be added to the OpenUPM ecosystem. Google about it to find out more, but it's very cool!