Add HAProxy to Glossary

Add link to plone/plone-haproxy

Author: stevepiercy

docs/glossary.md

@@ -297,4 +297,7 @@ ZEO
 
 PostgreSQL
     [PostgreSQL](https://www.postgresql.org/) is a powerful, open source object-relational database.
+
+HAProxy
+    [HAProxy](https://www.haproxy.org/) is a free, very fast and reliable reverse-proxy offering high availability, load balancing, and proxying for TCP and HTTP-based applications.
 ```

docs/install/containers/examples/haproxy-plone-zeo.md

@@ -10,7 +10,9 @@ html_meta:
 
 Very simple setup with only one or more backend instances accessing a ZEO server and data being persisted in a Docker volume.
 
-HAProxy is used for load balancing in this example.
+{term}`HAProxy` is used for load balancing in this example.
+We will use the image [`plone/plone-haproxy`](https://github.com/plone/plone-haproxy).
+
 
 ## Setup