TCP input TLS - Update README.

Author: BonnyAD9

src/plugins/input/tcp/README.rst

@@ -12,6 +12,9 @@ initial period of inability to interpret flow records does not apply here.
 Received IPFIX messages may be compressed using LZ4 stream compression. The compression is
 enabled on the exporter and the plugin detects it automatically.
 
+Received IPFIX messages may be secured with TLS. The TLS decoder is enabled by specifying the
+certificateFile parameter. Inbound TLS messages are automatically detected.
+
 Example configuration
 ---------------------
 
@@ -39,6 +42,12 @@ Mandatory parameters:
     multiple times (one IP address per occurrence) to manually select multiple interfaces.
     [default: empty]
 
+Optional parameters:
+
+:``certificateFile``:
+    Absolute path to a PEM file with certificate and private key. Specifying this path will enable
+    TLS decoder for the inbound connections. If this parameter is omitted, TLS decoder is disabled.
+
 Notes
 -----
 The LZ4 compression uses special format that compatible with