Update relabel.Process comment

Signed-off-by: Douglas Camata <159076+douglascamata@users.noreply.github.com>

model/relabel/relabel.go

@@ -188,10 +188,12 @@ func (re Regexp) String() string {
 	return str[4 : len(str)-2]
 }
 
-// Process returns a relabeled copy of the given label set. The relabel configurations
+// Process returns a relabeled version of the given label set. The relabel configurations
 // are applied in order of input.
+// There are circumstances where Process will modify the input label.
+// If you want to avoid issues with the input label set being modified, at the cost of
+// higher memory usage, you can use lbls.Copy().
 // If a label set is dropped, nil is returned.
-// May return the input labelSet modified.
 func Process(lbls labels.Labels, cfgs ...*Config) labels.Labels {
 	lb := labels.NewBuilder(nil)
 	for _, cfg := range cfgs {