[WIP] Add docs for NEST SSL
This PR is stale because it has been open for 14 days with no activity. Remove stale label or comment or update or this will be closed in 7 days. Dear Dr Huang, how to finetune the NEST model  with CTC loss function using nemo toolkit?
# What does this PR do ?


**place holder, will update later**

Add docs for NEST SSL

**Collection**: [asr]

