Add Gerrit v3.1 presentation

The Gerrit v3.1 release happened in Sunnyvale CA, just before
the Gerrit User Summit 2019: add link to the slides.

Change-Id: I7ef9516d2b7755a1556c5ac684d854a6d30121e8
diff --git a/pages/site/community/presentations.md b/pages/site/community/presentations.md
index 02ee188..d5d7051 100644
--- a/pages/site/community/presentations.md
+++ b/pages/site/community/presentations.md
@@ -35,6 +35,7 @@
 ## Release Highlights
 
 * [What's new in Gerrit 3.2/3.3?](https://drive.google.com/file/d/13T7CiQG54CZ7P6iqMYsFIV4P4dOV78iN/view) (2020)
+* [What's new in Gerrit 3.1 and beyond](https://www.slideshare.net/lucamilanesio/whats-new-in-gerrit-code-review-v31-and-beyond) (2019)
 * [What's new in Gerrit 3.0?](https://www.slideshare.net/lucamilanesio/whats-new-in-gerrit-code-review-30) (2019)
 * [What's new in Gerrit 2.14.x and 2.15?](https://storage.cloud.google.com/gerrit-talks/summit/2018/whats-new-in-2.14-and-2.15-gus-2018.pdf) (2018)
 * [Gerrit 2.16, 3.0, and beyond](https://storage.googleapis.com/gerrit-talks/summit/2018/Gerrit-2.16-3.0-and-Beyond.pdf) (2018)