fix typo (#297)

README.md

@@ -90,7 +90,7 @@ Which does not come with any desktops or window managers:
 
 ## Verification
 
-These images are signed with sisgstore's [cosign](https://docs.sigstore.dev/cosign/overview/). You can verify the signature by downloading the `cosign.pub` key from this repo and running the following command:
+These images are signed with sigstore's [cosign](https://docs.sigstore.dev/cosign/overview/). You can verify the signature by downloading the `cosign.pub` key from this repo and running the following command:
 
     cosign verify --key cosign.pub ghcr.io/ublue-os/silverblue-main