Add how to skip the change file check to pull request template
* [ ] Tests pass on CI and coverage remains at 100%
* [ ] Documentation reflects the changes where applicable
* [ ] `changes/<pull request or issue id>-<github username>.md` file added describing change
- (see [changes/README.md](https://github.com/pydantic/pydantic/blob/main/changes/README.md) for details)
+ (see [changes/README.md](https://github.com/pydantic/pydantic/blob/main/changes/README.md) for details.
+ You can [skip this check](https://github.com/pydantic/hooky#change-file-checks) if the change does not need a change file.)
* [ ] My PR is ready to review, **please add a comment including the phrase "please review" to assign reviewers**
