roadmap: link to the magic spreadsheet

roadmap/2025.md

@@ -85,6 +85,10 @@ event, but is now part of our roadmap.
 
 - Plan was made in [2025-01-13](meeting/2025-01-13)
 
+# Capacity tracking
+
+Actual quarterly allocations are managed in a [Nextcloud spreadsheet](https://nc.torproject.net/apps/onlyoffice/458448).
+
 # References
 
 This roadmap was discussed in November 2024 in two meetings,