You download and launch Obtanium. You tap on 'Add App'. You copy/paste https://voiceinput.futo.org/ into the 'App Source URL' field and click on 'Add'. Now, this might take some time, maybe a few minutes. Then you should be able to install the app. Obtanium will notify you whenever an update is released, and it will also allow you to download and install the new version.
You download and launch Obtanium. You tap on 'Add App'. You copy/paste https://voiceinput.futo.org/ into the 'App Source URL' field and click on 'Add'. Now, this might take some time, maybe a few minutes. Then you should be able to install the app. Obtanium will notify you whenever an update is released, and it will also allow you to download and install the new version.