Update README.md

Author: ellessenne

README.md

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 # GSWEP4R Short Course @ ISCB 2025, Basel, Switzerland, August 2025
 
 Sources and materials for the *"Good Software Engineering Practice for R Packages"* pre-conference course at ISCB 2025 in Basel, Switzerland.
-The course is scheduled for August 24^th^, 2025.
+The course is scheduled for August 24<sup>th</sup>, 2025.
 
 - [GSWEP4R Short Course Website](https://openstatsware.github.io/shortcourse-iscb2025/)