Add explicit reference to BGPSec support.

source/index.rst

@@ -93,6 +93,7 @@ line and through an API.
    ca-keyroll
    ca-migrate-repo
    hsm
+   manage_bgpsec
 
 .. toctree::
    :maxdepth: 2

source/manage-bgpsec.rst

@@ -0,0 +1,17 @@
+.. _doc_krill_manage_bgpsec:
+
+Manage BGPSec Router Certificates
+=================================
+
+Krill supports signing :RFC:`8209` BGPSec Router Certificates as of
+release 0.10.0. These certificates are used publish the router keys for
+:RFC:`8205` BGPSec protocol capable routers. Unfortunately, this protocol
+is not (yet) supported by many routers. We hope that by adding support
+for signing router certificates to the Krill CLI and API we can help
+support the future development and deployment of BGPSec. However,
+because BGPSec deployment is still lacking we have chosen not to support
+this in the UI at this time. But, of course, we are more than willing to
+add this in future if BGPSec deployment takes off and / or there is user
+demand for this.
+
+The CLI commands are documented :ref:`here<cmd_krillc_bgpsec>`.