On Linux, access to USB devices by ordinary users isn't automatically granted.
There's supposed to be a rules file installed in /etc/udev/rules.d/10-usrp.rules
I don't know how the UHD installer in Pybombs copes with this, since there's no way to conveniently have this user-managed, in your own home
In your src directory under pybombs, look for uhd/host/utils/uhd-usrp.rules and copy that to the location Marcus mentioned. Here are some of the setup commands from Ettus’s documentation.
sudo cp uhd-usrp.rules /etc/udev/rules.d/
sudo udevadm control --reload-rules
sudo udevadm trigger