Multilingual Training Notebook: Allowing users to continue previous training from checkpoint file

[isaquecsilva]

Changes to piper_multilingual_training_notebook.ipynb:

Users can now continue previous model training by providing a Google Drive share link to the .ckpt file of the previous training.

File Changes:

• On section 6 (training time), i added a text input field for the user to be providing a Google drive link to the checkpoint file;

• Python code will just download the .ckpt file, put it in previous-checkpoint dir (code will create it), and build --resume_from_checkpoint or --resume_from_single_speaker_checkpoint cli argument, pointing to the downloaded checkpoint file and add it to the piper_train execution line;

Check changes made here:

https://colab.research.google.com/github/isaquecsilva/piper/blob/training-with-checkpoint/notebooks/piper_multilingual_training_notebook.ipynb