diff --git a/README.md b/README.md
index 10f9d0e..63088af 100644
--- a/README.md
+++ b/README.md
@@ -75,6 +75,7 @@ The manifest file would do several important things:
     * (fetches `https://example.com/manifestdirectory/index.mf`, downloads and checksums all files, resumes any that exist locally already)
 * `mfer fetch https://example.com/manifestdirectory/`
 * a command line option to zero/omit mtime/ctime, as well as manifest timestamp, and sort all directory listings so that manifest file generation is deterministic/reproducible
+* URL format `mfer fetch https://exmaple.com/manifestdirectory/?key=5539AD00DE4C42F3AFE11575052443F4DF2A55C2` to assert in the URL which PGP signing key should be used in the manifest, so that shared URLs have a cryptographic trust root
 
 # Use Cases