## What was done?
Add builder key for @knst
## How Has This Been Tested?
It is the same file with:
https://github.com/dashpay/guix.sigs/blob/master/builder-keys/knst.pgp
Checked a signature of guix.sigs for 20.0.2: `gpg --status-fd 1 --verify
20.0.2/knst/codesigned.SHA256SUMS.asc` - matched.
## Breaking Changes
N/A
## Checklist:
- [x] I have performed a self-review of my own code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have added or updated relevant unit/integration/functional/e2e
tests
- [ ] I have made corresponding changes to the documentation
- [x] I have assigned this pull request to a milestone
