readme DOC missing optional libpam dependency
Refs
@@ -67,6 +67,7 @@ the `distro` directory.
#### Optional
+* libpam (for PAM-based SSH `keyboard-interactive` authentication method)
* libval (only for DNSSEC SSHFP retrieval)
* [DNSSEC-Tools/dnssec-tools/validator](https://github.com/DNSSEC-Tools/DNSSEC-Tools/tree/master/dnssec-tools/validator)
part of the DNSSEC-Tools suite
