US4_a: model metrics

[AlbaGarciaRomo]

US4_a: As a Data Scientist I want to monitor the model through metrics so that I can choose which model is better.

Acceptance Criteria:

• Investigate different evaluation methods for the recommender (Know/ summarise different methods and their relevance for the case). Write a document that is stored in the Documentation folder
• We have access to the key metrics (that are given in the Spotlight library), including MRR score, precision, and recall, for monitoring of the Recommender system's performance. We can choose what model is performing better.

Size: 20

[AlbaGarciaRomo]

This user story, was started in sp1, and it continues to sp2