Update README.rst

[yjeanrenaud]

timestamp is not a method but a property

Pull Request Checklist

• [na ] 🧪 Added tests for changed code.
• [na] 🛠️ All tests pass when run locally (run tox or make test to find out!).
• [na ] 🧹 All linting checks pass when run locally (run tox -e lint or make lint to find out!).
• 📚 Updated documentation for changed code.
• [na] ⏩ Code is up-to-date with the master branch.

Description of Changes

i just changed a small typo in the readme that bugged me

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (403c29f) to head (23a3737).
Report is 14 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #1204   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines         2324      2334   +10     
  Branches       357       357           
=========================================
+ Hits          2324      2334   +10     

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