Update SAR+ README

[simonzhaoms]

Description

The SAR+ README is out-of-dated. This PR updated and corrected the README.

Related Issues

Checklist:

• I have followed the contribution guidelines and code style for this project.
• I have added tests covering my contributions.
• I have updated the documentation accordingly.
• This PR is being made to staging branch and not to main branch.

[codecov-commenter]

Codecov Report

Merging #1682 (eafdf5b) into staging (93c9df2) will increase coverage by 23.20%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           staging    #1682       +/-   ##
============================================
+ Coverage     0.00%   23.20%   +23.20%     
============================================
  Files           88       88               
  Lines         9101     9101               
============================================
+ Hits             0     2112     +2112     
- Misses           0     6989     +6989     

Flag	Coverage Δ
nightly	?
pr-gate	23.20% <ø> (?)

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Impacted Files	Coverage Δ
recommenders/datasets/mind.py	0.00% <0.00%> (ø)
recommenders/datasets/movielens.py	66.37% <0.00%> (+66.37%)	⬆️
recommenders/datasets/download_utils.py	90.00% <0.00%> (+90.00%)	⬆️
recommenders/models/newsrec/io/mind_iterator.py	0.00% <0.00%> (ø)
recommenders/models/newsrec/models/base_model.py	0.00% <0.00%> (ø)

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