Correct README's reference to nilaway

[danielgospodinow]

Motivation / Background

This Pull Request has been created to correct the README where it links the nilaway CLI. It mistakenly had a link to the current repository.

Additional information

Checklist

Before submitting the PR, make sure the following are checked:

• Version file (/.version) is updated according to the
  Semantic Version rules.
• This Pull Request is related to one change.
  Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why.
  If this PR fixes a related issue, include it in the commit message.
  Ex: [Fixes #issue-number].
• Tests are added or updated if you fix a bug or add a feature.