update fields description

Signed-off-by: Tetiana Kravchenko <tetiana.kravchenko@elastic.co>

metricbeat/module/kubernetes/pod/_meta/fields.yml

@@ -56,7 +56,7 @@
               type: scaled_float
               format: percent
               description: >
-                CPU usage as a percentage of the defined cpu limits sum of the pod containers. If one or more containers of the pod is unlimited, this metric will be missing entirely.
+                CPU usage as a percentage of the defined cpu limits sum of the pod containers. If any container is missing a limit the metric is not emitted.
     - name: memory
       type: group
       fields:
@@ -77,7 +77,7 @@
               type: scaled_float
               format: percent
               description: >
-                Memory usage as a percentage of the defined memory limits sum of the pod containers. If one or more containers of the pod is unlimited, this metric will be missing entirely.
+                Memory usage as a percentage of the defined memory limits sum of the pod containers. If any container is missing a limit the metric is not emitted.
         - name: available
           type: group
           fields:
@@ -98,7 +98,7 @@
               type: scaled_float
               format: percent
               description: >
-                Working set memory usage as a percentage of the defined limits sum of the pod containers. If one or more containers of the pod is unlimited, this metric will be missing entirely.
+                Working set memory usage as a percentage of the defined limits sum of the pod containers. If any container is missing a limit the metric is not emitted.
         - name: rss
           type: group
           fields: