Update Symposium_SIESTA_2025.md

Author: arnodelorme

Diff for: workshops/Symposium_SIESTA_2025.md

@@ -15,9 +15,9 @@ Registration
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 There is no cost. However, if you want lunch, please email [Adrien](mailto:adrien.romain.marque@gmail.com). 
 
-Location
+Location and date
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-Toulouse CerCo laboratory, [Baudot building, first floor conference room (not ground floor)](https://cerco.cnrs.fr/en/visit-us/)
+June 30th, 2025, Toulouse CerCo laboratory, [Baudot building, first floor conference room (not ground floor)](https://cerco.cnrs.fr/en/visit-us/)
 
 Program
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