Fix header level in Audio docs
_The documentation is not available anymore as the PR was closed or merged._
Fixes header level so `Dataset features` is the doc title instead of `The Audio type`:

![Screen Shot 2022-10-05 at 1 22 02 PM](https://user-images.githubusercontent.com/59462357/194155840-eeb5d62f-f4eb-411e-b281-8494c5fffdce.png)