Fix POT link in README.md

[matbesancon]

The link was pointing to the book, not to the POT package

[devmotion]

A good catch! A bit surprising given that the correct link is used further down in the README 😄

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.28%. Comparing base (9da044c) to head (dc408ff).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #193      +/-   ##
==========================================
- Coverage   95.30%   94.28%   -1.02%     
==========================================
  Files          14       14              
  Lines         681      683       +2     
==========================================
- Hits          649      644       -5     
- Misses         32       39       +7     

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[coveralls]

Pull Request Test Coverage Report for Build 16784290562

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.29%

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Totals
Change from base Build 16783098803:	0.0%
Covered Lines:	644
Relevant Lines:	683

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💛 - Coveralls