fix: clean up sbkey warning message

Make a markdown link so it reads better when rendered.

system_files/shared/usr/libexec/check-sb-key.sh

@@ -5,7 +5,7 @@ if [ "$(id -u)" -ne 0 ]; then
   exit 1
 fi
 
-WARNING_MSG="This machine has secure boot turned on, but you haven't enrolled Universal Blue's keys. Failing to enroll these before rebooting **may cause your system to fail to boot**. Follow this link https://docs.projectbluefin.io/introduction#secure-boot ~for instructions on how to enroll the keys."
+WARNING_MSG="This machine has secure boot turned on, but you haven't enrolled Universal Blue's keys. Failing to enroll these before rebooting **may cause your system to fail to boot**. Follow [the documentation](https://docs.projectbluefin.io/introduction#secure-boot) ~for key enrollment information."
 KEY_WARN_FILE="/run/user-motd-sbkey-warn.md"
 KEY_DER_FILE="/etc/pki/akmods/certs/akmods-ublue.der"