chore: add pdf and link to it in summit page

Author: andrea-kyurchiev

content/en/events/isc-2025.md

@@ -98,7 +98,7 @@ September – Communication from the InnerSource Commons Summit team on status u
 
 ## Why Sponsor?
 
-**[Unlock Exclusive Sponsorship Opportunities]()**
+**[Unlock Exclusive Sponsorship Opportunities](/documents/innersource_commons_sponsorpresentation.pdf)**
 
 
 We sincerely appreciate your interest in sponsoring the InnerSource Commons Summit 2025. This landmark event celebrates our 10th anniversary and will take place simultaneously across three global locations - Yokohama, Berlin, and New York - on Thursday, November 13th, 2025.