docs: fix Decode godoc (#188)

codecs.go

@@ -16,7 +16,7 @@ type Codec interface {
 	// There must be no missing shares. Only returns parity shares.
 	Encode(data [][]byte) ([][]byte, error)
 	// Decode decodes sparse original + parity data, automatically extracting share size.
-	// Missing shares must be nil. Returns original shares only.
+	// Missing shares must be nil. Returns original + parity data.
 	Decode(data [][]byte) ([][]byte, error)
 	// maxChunks returns the max. number of chunks each code supports in a 2D square.
 	maxChunks() int