docs: add hash footnote

[AngryMaciek]

Description

Add a footnote regarding the follow-up hashing research.

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] I have not reduced the existing code coverage

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (a8eee3f) 100.00% compared to head (5ed966c) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #40 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 2 2 Lines 673 673 ========================================= Hits 673 673 ```

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