People can join you with their web browser
If they don't have the Drovio app installed, people can join you from Slack with their web browser without having to download or configure anything and thus get straight into action!
Additional slash commands
In addition to the /drovio command, you can also use the /drovio invite or /drovio add commands to respectively invite someone to join your session or add them to your contact list.
Note that you need to have the Drovio app installed before using any of these commands. You can get a list of all the available commands and parameters with /drovio help.