Add link to PAC slides in README.md

README.md

@@ -3,6 +3,9 @@
 This project contains the configuration for the LHCb software stacks, and the
 software to present this metadata in the format required by the build tools.
 
+For some context and introduction to the concept of stacks, please see
+[these slides](https://indico.cern.ch/event/1018357/contributions/4279996/attachments/2211976/3743760/New%20release%20deployment%20procedure%20and%20tools.pdf).
+
 ## Project structure
 
   - `data`: directory structure containing the LHCb stack definitions in YAML format