Nexus 5 stuck at Google screen after failed(?) rooting
This solved the problem:


Download the latest stable SuperSU, it is the ZIP file that can be downloaded at http://download.chainfire.eu/supersu-stable
Restart in TWRP Recovery mode
Press Mount
Delete the faulty ZIP and copy the right one instead (at the root of the filesystem)
Fixed! Now continue with the tutorial normally.


Thanks rjt.rockx and eldarerathis for the tips!