Adding link to San Diego CS testgrid presentation

Signed-off-by: markyjackson-taulia <[email protected]>

Author: markjacksonfishing

contributors/devel/sig-testing/testing.md

@@ -257,6 +257,7 @@ For known flakes (i.e. with open GitHub issues against them), the community deep
 It is useful as a way to:
 - see the run history of a test you are debugging (access it starting from a gubernator report for that test)
 - get an overview of the project's general health
+- You can learn more about Testgrid from the [Kubecon NA San Diego Contributor Summit](https://youtu.be/8xS6mmGhbIQ)
 
 `testgrid` is organised in:
 - tests