docs:monitor: Fill in trust group class attribute details

The `class` attribute within 'sensor_trust_groups' contains the trust
group determination class implementation to use in determining trust of
the fan sensors within the trust group.

Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
Change-Id: I52721974a8af61f2bb912751a016dfcd28d824e6
diff --git a/docs/monitor/class.md b/docs/monitor/class.md
index 32fe3e9..5972c03 100644
--- a/docs/monitor/class.md
+++ b/docs/monitor/class.md
@@ -1,9 +1,38 @@
 # class
 
 ## Description
-
+A trust group determination class that implements a way to check a group of fan
+sensors trust state. Each of these 'classes' override a required function that
+determines if the group is trusted by checking each fan sensors listed within
+the trust group against an algorithm that returns whether they can be trusted
+or not.
 
 ## Attribute Value(s)
-
+* `NonzeroSpeed`
+  * Determines if the group is trusted by checking if any sensors in the group
+  has a nonzero speed. If all sensors report zero, then no sensors in the group
+  are trusted and therefore monitoring of all the sensors in the group is
+  canceled.
 
 ## Example
+<pre><code>
+{
+  "sensor_trust_groups": [
+    {
+      <b><i>"class": "NonzeroSpeed"</i></b>,
+      "group": [
+        {
+          "name": "fan0_0"
+        },
+        {
+          "name": "fan1_0"
+        },
+        {
+          "name": "fan2_0",
+          "in_trust": false
+        }
+      ]
+    }
+  ]
+}
+</code></pre>