text: Title: Unclear information in Explained variance
  Body: ### Describe the issue linked to the documentation
  
  Hi, the text in Explained variance page is somewhat unclear, so I want to propose a clearer text. On line 1005, the detail says this:
  
  > "The Explained Variance score is similar to the R^2 score, with the notable difference that it does not account for systematic offsets in the prediction. Most often the R^2 score should be preferred."
  
  
  
  ### Suggest a potential alternative/fix
  
  I propose to change it like this:
  
  > "The Explained Variance score is similar to the R^2 score, with the notable difference that **R^2 score also accounts for systematic offsets in the prediction (i.e., the intercept of the linear function). This means that R^2 score changes with different systematic offsets, whereas  Explained Variance does not.** Most often the R^2 score should be preferred."