Changelog: explanation about normalize in 5.5.0 not clear

[rlanzafame]

The changelog for 5.5.0 suggests that a better alternative to the normalize function is available, but does not state what that is.

I got a MissingIDFieldWarning warning:

...\Lib\site-packages\nbformat\__init__.py:96: MissingIDFieldWarning: Cell is missing an id field, this will become a hard error in future nbformat versions. You may want to use `normalize()` on your notebooks before validations (available since nbformat 5.1.4). Previous versions of nbformat are fixing this issue transparently, and will stop doing so in the future.
  validate(nb)

I understand that the normalize() function is a workaround, for example, the discussion in #359

Specifically, I think the lines here in CHANGELOG.md should be clarified:

`nbformat` now contain a `normalize` function that will return a
normalized copy of a notebook that is suitable for validation. While
offered as a convenience we discourage its use and suggest library make
sure to generate valid notebooks.

I am new to this stuff, but am happy to try and set up a PR; however, I do not know what the preferred approach is!

[rlanzafame]

nbformat v5.10.4