Minor updates to documentation in filter.h

[JiaT75]

Pull request checklist

Please check if your PR fulfills the following requirements:

• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been reviewed and added / updated if needed (for bug fixes / features)
• [X] Build was run locally and without warnings or errors
• [X] All previous and new tests pass

Pull request type

Please check the type of change your PR introduces: - [ ] Bugfix - [ ] Feature - [ ] Code style update (formatting, renaming, typo fix) - [ ] Refactoring (no functional changes, no api changes) - [ ] Build related changes - [X] Documentation content changes - [ ] Other (please describe): ## Does this introduce a breaking change? - [ ] Yes - [X] No