A certificate for web browsers is available here.

Installation:
For Linux you can use an installer for Debian-based distros (link here) and for Arch-based distros (link here). Eventually you can follow the instructions of how to install a custom CA for your distro.

For Windows there's a batch file installer. You can run it through cmd.exe or by clicking on it.

For Mac OS X you will need to download a certificate file, open it with your file explorer and in the popup menu, press Always Trust.

For Android you will need to download a certificate file,
go to the device settings -> Security -> Encryption & Credentials -> Install from storage -> Install a certificate -> select CA Certificate -> Pick the downloaded certificate and add it.