doc/filters: update URL for sr filter script repository

Because the Original repository author loss loss of communication,
add new sr filter script repository.

Thanks to Gyan Doshi for a suggestion.
Signed-Off-By: Steven Liu <lq@chinaffmpeg.org>

doc/filters.texi

@@ -16537,8 +16537,9 @@ Efficient Sub-Pixel Convolutional Neural Network model (ESPCN).
 See @url{https://arxiv.org/abs/1609.05158}.
 @end itemize
 
-Training scripts as well as scripts for model generation are provided in
-the repository at @url{https://github.com/HighVoltageRocknRoll/sr.git}.
+Training scripts as well as scripts for model generation can be found at
+@url{https://github.com/XueweiMeng/sr/tree/sr_dnn_native}. Original repository
+is at @url{https://github.com/HighVoltageRocknRoll/sr.git}.
 
 The filter accepts the following options: