Update kubernetes filter docs (fluent#48)

* Update kubernetes filter docs

* Update buffer_size description in Kubernetes filter docs

filter/kubernetes.md

@@ -22,7 +22,13 @@ The plugin supports the following configuration parameters:
 
 | Key         |  Description             | Default                            |
 | ------------|--------------------------|------------------------------------|
+| Buffer\_Size | Set the buffer size for HTTP client when reading responses from Kubernetes API server. The value must be according to the [Unit Size](../configuration/unit_sizes.md) specification. | 32k |
 | Kube\_URL       | API Server end-point  | https://kubernetes.default.svc:443 |
 | Kube\_CA\_File | CA certificate file   | /var/run/secrets/kubernetes.io/serviceaccount/ca.crt|
+| Kube\_CA\_Path | CA path |  |
 | Kube\_Token\_File | Token file | /var/run/secrets/kubernetes.io/serviceaccount/token |
-| Merge\_JSON\_Log | When enabled, it checks if the _log_ field content is a JSON string map, if so, it append the map fields as part of the log structure. | Off |
+| Merge\_JSON\_Log | When enabled, it checks if the `log` field content is a JSON string map, if so, it append the map fields as part of the log structure. | Off |
+| Merge\_JSON\_Key | When `Merge_JSON_Log` is enabled, the filter tries to assume the `log` field from the incoming message is a JSON string message and make a structured representation of it at the same level of the `log` field in the map. Now if `Merge_JSON_Key` is set (a string name), all the new structured fields taken from the original `log` content are inserted under the new key. |  |
+| tls.debug | Debug level between 0 (nothing) and 4 (every detail). | -1 |
+| tls.verify | When enabled, turns on certificate validation when connecting to the Kubernetes API server. | On |
+| Use\_Journal | When enabled, the filter reads logs coming in Journald format. | Off |