Ok, I wanted to give this a try.
TL;DR: in 5 minutes I had this:
HOWTO
This is my system:
arch x86_64
dev false
docker true
hassio true
os_name Linux
os_version 5.3.0-28-generic
python_version 3.7.7
version 0.107.6
virtualenv false
My prerrequisites:
- I have MQTT enabled
- I also have zigbee2mqtt
- I use HACS to install the zigbee2mqtt map
My steps:
1.- Search zigbee2mqtt in the Integrations tab in HACS:

2.- Click install (the screenshot shows reinstall because I’m writing this howto after installing it):

3.- I added this to my configuration.yaml :
zigbee2mqtt_networkmap:
topic: zigbee2mqtt
panel_iframe:
networkmap:
title: 'Zigbee Map'
url: '/local/community/zigbee2mqtt_networkmap/map.html'
icon: 'mdi:graphql'
It’s the same as in the instructions in the add-on but, as @cdef said, the indentations are off.
4.- Restart HA
5.- Go to Developers tools and run the zigbee2mqtt_networkmap.update service:

6.- Enjoy the map clicking in the sidebar:

Thanks to all the people that make this possible.
