Restore text about sig validity and SOA expire

When `sig-validity-interval` was obsoleted, the text that the signature
validity interval should be multiples of the SOA expire interval was
removed. Restore this text to the description of the
`signatures-validity` option.

(cherry picked from commit b09230004bf7e64fe678851854bf4044f52c72c1)

diff --git a/doc/arm/reference.rst b/doc/arm/reference.rst
index 293e7ca58139894405e14385cae8a10b93930843..88a44045ba9b8d568ce872d726055f0a0dc3ad5c 100644 (file)
--- a/doc/arm/reference.rst
+++ b/doc/arm/reference.rst
@@ -6642,6 +6642,10 @@ keys
     This indicates the validity period of an RRSIG record (subject to
     inception offset and jitter). The default is ``P2W`` (2 weeks).
 
+    The :any:`signatures-validity` should be at least several multiples
+    of the SOA expire interval, to allow for reasonable interaction between
+    the various timer and expiry dates.
+
 .. namedconf:statement:: signatures-validity-dnskey
    :tags: dnssec
    :short: Indicates the validity period of DNSKEY records.