Update model file extension (#1422)

* Update model file ext to ```.pth```

* Update docs

* Rename more

* Find model files

docs/source/tutorial_for_nervous_beginners.md

@@ -50,13 +50,13 @@ A breakdown of a simple script that trains a GlowTTS model on the LJspeech datas
     - Fine-tune a model.
 
         ```bash
-        CUDA_VISIBLE_DEVICES=0 python train.py --restore_path path/to/model/checkpoint.pth.tar
+        CUDA_VISIBLE_DEVICES=0 python train.py --restore_path path/to/model/checkpoint.pth
         ```
 
     - Run multi-gpu training.
 
         ```bash
-        CUDA_VISIBLE_DEVICES=0,1,2 python TTS/bin/distribute.py --script train.py
+        CUDA_VISIBLE_DEVICES=0,1,2 python -m trainer.distribute --script train.py
         ```
 
 ### CLI Way