fix(readme): Update Mnestix URL

[hofermo]

Description

Please include a summary of the changes and link the related github issue. Please include relevant motivation and context.

Fixes # (Issue)

Type of change

Please delete options that are not relevant.

• [x] Minor change (non-breaking change, e.g. documentation adaption)

Checklist:

• [x] I have performed a self-review of my code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [ ] I have added tests that prove my fix or my feature works
• [ ] New and existing tests pass locally with my changes
• [ ] My changes contain no console logs

[hofermo]

As we moved our domains over to the Eclipse Foundation, mnestix.io and mnestix.com are or will temporarely not work. Once we set it up again, this change can be reverted :)

[Xmilofranke]

I guess the link on the home page of the browser also has to be adjusted

[hofermo]

Closed as mnestix.io works again