[DOC] Add a reference for MERLIN anomaly detector

[TonyBagnall]

Describe the issue linked to the documentation

we recently added the MERLIN anomaly detection algorithm but there is no reference to the original paper

https://ieeexplore.ieee.org/document/9338376

need to add this to the docstrings

Suggest a potential alternative/fix

No response

[TonyBagnall]

fixed by
#1707