start node maintenance docs

Signed-off-by: Ryan Goodfellow <rgoodfel@isi.edu>

docs/node-maintenance.md

+---
+id: node-maintenance
+title: Node Maintenance
+---
+
+This page describes how to conduct common node maintenance tasks in a Merge
+facility.
+
+## Power Control
+
+Merge testbed facilities have a centralized node power control service called
+[Beluga](https://gitlab.com/mergetb/tech/beluga). 
+
+![](/img/node-maintenance/beluga.svg)
+
+Beluga is an abstraction layer that hides the details of controlling the power
+of devices through PDU, IPMI/Redfish or hypervisor specific mechanisms.
+
+Usage of the `beluga` utility is straight forward.
+
+```
+beluga -h
+```
+```
+Beluga client utility
+
+Usage:
+  beluga [command]
+
+Available Commands:
+  cycle       Cycle a device
+  help        Help about any command
+  list        List devices
+  off         Turn off a device
+  on          Turn on a device
+  status      Get device power status
+  version     Show beluga version
+
+Flags:
+  -h, --help   help for beluga
+
+Use "beluga [command] --help" for more information about a command.
+```
+
+- `cycle` will turn a node off, wait for a short period then turn it on.
+- `off` will turn a node off
+- `on` will turn a node on
+
+The power status of nodes may be queried via `status`
+
+You can also show all available devices and what their underlying power control
+mechanism is.
+
+```
+beluga list
+```
+```
+a0    ipmi
+a1    ipmi
+a2    ipmi
+a3    ipmi
+m0    minnow
+m1    minnow
+mc0   apc
+mc1   apc
+n0    apc
+n1    apc
+n2    apc
+```

sidebars.js

@@ -33,6 +33,7 @@ module.exports = {
     ],
     'Facility Operations': [
         'facility',
+        'node-maintenance',
         'package-server',
         'cert-management',
     ],