Add new deadline based on ISC 2025 and SC25 dates

Author: luszczek

hpl-mxp.org/upload.md

@@ -5,4 +5,8 @@ Upload Results
 The results can be uploaded through an
 [external form](https://docs.google.com/forms/d/e/1FAIpQLSetOEKVSDWA5k-YRZHqIPKO9XO0Oyyld7-i0jHCan1MuXoJWA/viewform?usp=sf_link).
 
-The deadline for results to appear in ISC 2024 edition is April 30, 2024.
+The deadline for submitting results depends on the upcoming edition
+of the list. The following dates are used annually:
+
+* to appear in the ISC High Performance edition the deadline is May 15th.
+* to appear in the SC series edition the deadline is October 20th.