I followed the instructions at https://ooni.torproject.org/install/lepidopter and found a few errors.
It tells you how to gpg-verify the image, but not how to download the .asc signature itself.
The xz command has a .zip filename, not .xz: xz --decompress --verbose --no-sparse lepidopter-alpha-armel.img.zip
It says the login credentials are lepidopter/lepidopter, but doesn't say what to do with them. I guess there should be a hint at the bottom that the next thing to do is go to http://lepidopter.local/
The README.md file at https://github.com/TheTorProject/lepidopter also has a little bug, an extra "of=" in the bmaptool command: bmaptool copy --nobmap lepidopter-alpha-armel.img.xz of=/dev/diskX
After booting, my Raspberry Pi doesn't have a web interface (only port 22 is open).