[skip ci] Add comment for IFVConfAdapter (#13200)

Signed-off-by: shaoyue.chen <shaoyue.chen@zilliz.com>

internal/util/indexparamcheck/conf_adapter.go

@@ -143,6 +143,7 @@ type IVFConfAdapter struct {
 	BaseConfAdapter
 }
 
+// CheckTrain returns true if the index can be built with the specific index parameters.
 func (adapter *IVFConfAdapter) CheckTrain(params map[string]string) bool {
 	if !CheckIntByRange(params, NLIST, MinNList, MaxNList) {
 		return false