Self-certify for the CII best practices badge (Add diffoscope to bestpractices.coreinfrastructure.org)

from task list at: https://salsa.debian.org/reproducible-builds/reproducible-tasks/-/blob/88088ee53eb3caf071ce6e45d532601ffc18b5d3/pending.txt#L100

- https://bestpractices.coreinfrastructure.org/ for our own apps

More information about the program: https://bestpractices.coreinfrastructure.org/ https://github.com/linuxfoundation/cii-best-practices-badge

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information