Add Python API for clustering (#1385)

sherpa-onnx/csrc/fast-clustering-config.h

@@ -12,12 +12,23 @@
 namespace sherpa_onnx {
 
 struct FastClusteringConfig {
-  // If greater than 0, then threshold is ignored
+  // If greater than 0, then threshold is ignored.
+  //
+  // We strongly recommend that you set it if you know the number of clusters
+  // in advance
   int32_t num_clusters = -1;
 
-  // distance threshold
+  // distance threshold.
+  //
+  // The lower, the more clusters it will generate.
+  // The higher, the fewer clusters it will generate.
   float threshold = 0.5;
 
+  FastClusteringConfig() = default;
+
+  FastClusteringConfig(int32_t num_clusters, float threshold)
+      : num_clusters(num_clusters), threshold(threshold) {}
+
   std::string ToString() const;
 
   void Register(ParseOptions *po);