add note about bogons and resolution

internal/experiment/openvpn/targets.go

@@ -41,6 +41,12 @@ func sampleN(a []string, n int) []string {
 // performing DNS resolution. The returned IP addreses exclude possible
 // bogons.
 func resolveOONIAddresses(logger model.Logger) ([]string, error) {
+
+	// We explicitely resolve with BogonIsError set to false, and
+	// later remove bogons from the list. The reason is that in this way
+	// we are able to control the rate at which we run tests by adding bogon addresses to the
+	// domain records for the test.
+
 	resolver := netx.NewResolver(netx.Config{
 		BogonIsError: false,
 		Logger:       logger,