Update Summary with the new infra chapter

Author: dicortazar

SUMMARY.md

@@ -5,6 +5,7 @@
   * [Scenarios](introduction/scenarios.md)
   * [Framework](introduction/framework.md)
   * [Authors and Reviewers](introduction/authors.md)
+* [Infrastructure](infrastructure/infrastructure.md)
 * [What, When and How to Measure](measuring/introduction.md)
   * [Goals using Metrics](measuring/goals.md)
   * [Areas of Analysis](measuring/areas.md)