More docs.

README.md

@@ -81,6 +81,13 @@ for example:
 Assuming the messages that get printed are JSON, this print the sum of all age fields
 from each message in the partition.
 
+### Custom Decoder
+If your kafka messages are encoded in some way you can provide a custom decoder
+in the form of a plugin.  See plugins/protobuf for an example.  Once you have
+compiled the plugin you use it as the default decoder by starting kcli like so:
+
+    kcli -d /path/to/your/decoder.so
+
 ### Screen Colors
 
 If you don't like the defaul colors you can set KCLI_COLOR[0,1,2,3] to one of:

plugins/protobuf/protobuf.go

@@ -5,7 +5,12 @@ import (
 	"github.com/golang/protobuf/proto"
 )
 
-// Example of how to create a protobuf plugin for your data structure
+// Protobuf is an example of how to create a plugin
+// to decode protobuf encoded kafka messages.
+// To compile:
+//     go build -buildmode=plugin -o protobuf.so protobuf.go
+// Then start kcli like:
+//     kcli -d ./protobuf.so
 type Protobuf struct{}
 
 func (p Protobuf) Decode(b []byte) ([]byte, error) {