Qwen MoE model. (#1960)

* Qwen MoE model.

* Add the MoE model to the example.

* Fix the scaling.

* Readme updates.

* Readme tweaks.

candle-transformers/src/models/mod.rs

@@ -40,6 +40,7 @@ pub mod quantized_rwkv_v6;
 pub mod quantized_stable_lm;
 pub mod quantized_t5;
 pub mod qwen2;
+pub mod qwen2_moe;
 pub mod repvgg;
 pub mod resnet;
 pub mod rwkv_v5;