[Glossary: Light client] Make summary text aware of the differences to light nodes

[smuu]

https://celestia.org/glossary/light-client/

In summary on https://celestia.org/glossary/ it's written that a light client relies on an honest majority assumption. However, as stated in the expanded explanation Celesta light nodes do not make this assumption. Some will only read the summary, so we should point out there, that our light nodes do not make this assumption.