docs:monitor: Fill in trust group `group` attribute details

The `group` attribute within 'sensor_trust_groups' contains a list of
fan tach sensors to cancel/resume monitoring based on the trust
determination across all members of the group.

Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
Change-Id: Ifab450c05b7b8cde234d60b58eff1029ce66f5bb
diff --git a/docs/monitor/group.md b/docs/monitor/group.md
index 8a6ca2c..696f1f0 100644
--- a/docs/monitor/group.md
+++ b/docs/monitor/group.md
@@ -1,9 +1,35 @@
 # group
 
 ## Description
-
+A list of sensor object names to include in determining trust of their values based on the configured [`class`](class.md). These sensors are what's included in the group that then has all of their current values trusted or not for monitoring based on algorithm of the [`class`](class.md).
 
 ## Attribute Value(s)
-
+* `name` - string
+  * The name of the fan tach sensor located under the `/xyz/openbmc_project/sensros/fan_tach` D-Bus path.
+* `in_trust` - boolean (Optional)
+  * By default, the sensor is included in determining trust of the group.
+  However this can be used to cancel/restart monitoring of a fan tach sensor
+  but not have it included in the determination of trust.
 
 ## Example
+<pre><code>
+{
+  "sensor_trust_groups": [
+    {
+      "class": "NonzeroSpeed",
+      <b><i>"group": [
+        {
+          "name": "fan0_0"
+        },
+        {
+          "name": "fan1_0"
+        },
+        {
+          "name": "fan2_0",
+          "in_trust": false
+        }
+      ]</i></b>
+    }
+  ]
+}
+</code></pre>