message: docs: add `--nullish-coalescing` operator
diff: @@ -178,6 +178,7 @@ decaffeinate could be improved, feel free to file an issue on the [issues] page.
  - `--disallow-invalid-constructors`: Give an error when constructors use `this`
  before `super` or omit the `super` call in a subclass.
  - `--optional-chaining`: Target JavaScript optional chaining. Note the semantics may not match exactly.
  +- `--nullish-coalescing`: Target JavaScript [nullish coalescing](https://github.com/tc39/proposal-nullish-coalescing). Note the semantics may not match exactly.
  - `--logical-assignment`: Use the ES2021 [logical
  assignment](https://github.com/tc39/proposal-logical-assignment) operators
  `&&=`, `||=`, and `??=`.
  