[df][nfc] Update documentation of default colums with a Take example

Fixes #16487

tree/dataframe/src/RDataFrame.cxx

@@ -1203,8 +1203,9 @@ auto h = d1.Filter([](int b1, int b2) { return b1 > b2; }) // will act on "b1" a
 
 // just one default column this time
 RDataFrame d2("myTree", "file.root", {"b1"});
-auto min = d2.Filter([](double b2) { return b2 > 0; }, {"b2"}) // we can still specify non-default column lists
-             .Min(); // returns the minimum value of "b1" for the filtered entries
+auto d2f = d2.Filter([](double b2) { return b2 > 0; }, {"b2"}) // we can still specify non-default column lists
+auto min = d2f.Min(); // returns the minimum value of "b1" for the filtered entries
+auto vals = d2f.Take<double>(); // return the values for all entries passing the selection as a vector
 ~~~
 
 \anchor helper-cols