update readme: prometheus remote write (#8683)

plugins/serializers/prometheusremotewrite/README.md

@@ -1,4 +1,4 @@
-# Prometheus
+# Prometheus remote write
 
 The `prometheusremotewrite` data format converts metrics into the Prometheus protobuf
 exposition format.
@@ -13,11 +13,17 @@ use only the `prometheus_client` output.
 
 ```toml
 [[outputs.http]]
+  ## URL is the address to send metrics to
   url = "https://cortex/api/prom/push"
-  data_format = "prometheusremotewrite"
+  
+  ## Optional TLS Config
   tls_ca = "/etc/telegraf/ca.pem"
   tls_cert = "/etc/telegraf/cert.pem"
   tls_key = "/etc/telegraf/key.pem"
+  
+  ## Data format to output.
+  data_format = "prometheusremotewrite"
+  
   [outputs.http.headers]
      Content-Type = "application/x-protobuf"
      Content-Encoding = "snappy"