Update documentation related to "nbdev_release"

[bkowshik]

Ref: https://nbdev.fast.ai/tutorials/tutorial.html#upload-to-pypi-and-conda

Trying to make a release of my package using nbdev==2.3.7. But, I don't see any command called nbdev_release which is mentioned in the documentation. Instead, I see the below similar looking options:

$ nbdev_release
zsh: command not found: nbdev_release


# On hitting TAB, I see the following options.
$ nbdev_release_
nbdev_release_both  nbdev_release_gh    nbdev_release_git

[seeM]

I believe it should refer to nbdev_release_both

[seeM]

Fixed by #1215.