chore(contrib): add sm2 and move munin-syncthing to unmaintained (#912)

Add sm2 to the monitoring projects.
Move munin-syncthing to the Older, Possibly Unmaintained projects (last
updated 7 years ago).

Author: nware-lab

users/contrib.rst

@@ -251,7 +251,10 @@ Configuration management
 Monitoring
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
-- `munin-syncthing <https://gitlab.com/daftaupe/munin-syncthing>`_
+- `sm² (Syncthing Multi Server Monitor) <https://github.com/nware-lab/sm2>`_
+
+  A Docker container made to "monitor multiple Syncthing instances while using
+  as little diskspace & memory while doing it."
 
 Resolving conflicts
 ~~~~~~~~~~~~~~~~~~~
@@ -296,3 +299,4 @@ Older, Possibly Unmaintained
 -  https://github.com/nhojb/SyncthingBar
 -  https://github.com/jastBytes/SyncthingTray
 -  https://github.com/alex2108/syncthing-tray
+- `munin-syncthing <https://gitlab.com/daftaupe/munin-syncthing>`_