Add initial release notes for NAV 5.8

NOTES.rst

@@ -8,6 +8,57 @@ existing bug reports, go to https://github.com/uninett/nav/issues .
 To see an overview of upcoming release milestones and the issues they resolve,
 please go to https://github.com/uninett/nav/milestones .
 
+NAV 5.8
+=======
+
+Dependency changes
+------------------
+
+Upgrade your :mod:`pynetsnmp-2` library to at least version *0.1.10* to ensure
+SNMPv3 compatibility.
+
+SNMPv3
+------
+
+NAV 5.8 finally adds SNMPv3 support, although it is not yet 100%
+feature-complete.  A new management profile type has been added specifically
+for SNMPv3.  SNMPv3 management requires a host of configuration attributes,
+whereas v1/v2c only requires a community string.
+
+Additionally, if a device only has write-enabled SNMP management profiles
+attached to it, NAV will now try to use those also for read operations.  If
+your SNMPv3 profile supports both reading and writing, you should be able to
+get by with a single profile per device.
+
+
+Missing SNMPv3 features
+~~~~~~~~~~~~~~~~~~~~~~~
+
+**SNMPv3 traps**
+
+SNMPv3 trap support is still being worked on, but no working solution is
+available in 5.8.  See `issue #2755 for snmptrapd implementation and progress
+details <https://github.com/Uninett/nav/issues/2755>`.
+
+**SNMPv3 contexts**
+
+Various vendors use the concept of "community indexing" to fetch multiple
+logical instances of MIBs.  Examples include Cisco switches, where multiple
+instances of the ``BRIDGE-MIB`` are kept, one for each active VLAN.  To access
+the switch forwarding tables of VLAN 12 with an SNMP community of ``public``,
+the community must be modified to ``public@20``.
+
+Another common example is devices that allow SNMP management of individual VRF
+instances by modifying the SNMP community.
+
+However, since SNMPv3 does not use community strings, it instead provides the
+concept of "contexts", where the default context is typical an empty string.
+
+:program:`ipdevpoll` does not yet support using SNMPv3 contexts as a
+replacement for community indexing, so the types of data described above may be
+missing from some devices if switching them to SNMPv3.
+
+
 NAV 5.7
 =======