Add to manual how to install beta APK

Locus team requested to test latest beta. I went to https://docs.locusmap.app/doku.php/manual:about:free_beta_testing and checked

1. allow installing apps from other sources than Google Play in your phone system settings

is still allowed (AFAIK it's in "Unbekannte Apps installieren") for Total Commander, downloaded APK, clicked it in TC and when TC asks what to do

• I chose "install" – it tells the function is not supported and had to be removed on request from Google. It's so sad processes working for years are completely blocked instead just changed to increase security...
• I chose "Google Play" – Locus is installed, but after installation it tells v4.35.0 while beta APK file name carries v4.35.0.8 so Google Play version was installed.

I remember I used another help app than TC to install the beta APK on another device 1-2 years ago but can't recall the details. I now tried "Universal Installer" by NQM Innovation; when called from TC it reported the Locus APK is not processable, when calling the APK from "Universal Installer" it was installed.

Would be great if you could add more information on how to install the APK (or a link to an explanation) into the beta manual so not every user has to research again 🙂