[receiver/kubeletstats] Move metrics section to the top (#26291)

**Description:** 
I've received some internal feedback that unless you know what a kubelet
is, understanding which metrics the kubeletstatsreceiver collectors is
difficult. To make understanding this component easier I've adjusted the
initial tagline and moved the metrics documentation to the top.

receiver/kubeletstatsreceiver/README.md

@@ -15,9 +15,13 @@
 [sumo]: https://github.com/SumoLogic/sumologic-otel-collector
 <!-- end autogenerated section -->
 
-The Kubelet Stats Receiver pulls pod metrics from the API server on a kubelet
+The Kubelet Stats Receiver pulls node, pod, container, and volume metrics from the API server on a kubelet
 and sends it down the metric pipeline for further processing.
 
+## Metrics
+
+Details about the metrics produced by this receiver can be found in [metadata.yaml](./metadata.yaml) with further documentation in [documentation.md](./documentation.md)
+
 ## Configuration
 
 A kubelet runs on a kubernetes node and has an API server to which this
@@ -222,7 +226,3 @@ The following parameters can also be specified:
 
 The full list of settings exposed for this receiver are documented [here](./config.go)
 with detailed sample configurations [here](./testdata/config.yaml).
-
-## Metrics
-
-Details about the metrics produced by this receiver can be found in [metadata.yaml](./metadata.yaml) with further documentation in [documentation.md](./documentation.md)