Clarification of installation steps with Coral accelerator

M.2/PCI-e Coral accelerators use different device names to the USB accelerator. Additionally, while Coral is mentioned in other pages, it is not explicitly clear that this is not quite 'plug and play', which will trip up novice users.

The config file argument for docker needs to be a directory, not a file.

Added some other points to help clarify based on my first experience.

docs/docs/installation.md

@@ -9,6 +9,12 @@ For Home Assistant users, there is also a [custom component (aka integration)](h
 
 Note that HassOS Addons and custom components are different things. If you are already running Frigate with Docker directly, you do not need the Addon since the Addon would run another instance of Frigate.
 
+If you are running Frigate seperate to HassOS, you will need to install and configure an (https://mqtt.org/software/)[MQTT broker] such as (https://mosquitto.org/)[Mosquitto] first.
+
+Before using Frigate with a Coral accelerator, make sure that you have the edge TPU runtime installed. Click for instructions for the [USB accelerator](https://coral.ai/docs/accelerator/get-started/) or [M.2/Mini PCI-e accelerator](https://coral.ai/docs/m2/get-started/)
+
+A valid [configuration file](https://blakeblackshear.github.io/frigate/configuration/index/) must exist before starting Frigate.
+
 ## HassOS Addon
 
 HassOS users can install via the addon repository. Frigate requires an MQTT server.
@@ -46,7 +52,7 @@ services:
       - /dev/dri/renderD128 # for intel hwaccel, needs to be updated for your hardware
     volumes:
       - /etc/localtime:/etc/localtime:ro
-      - <path_to_config_file>:/config/config.yml:ro
+      - <path_to_config_directory>:/config:ro
       - <path_to_directory_for_media>:/media/frigate
       - type: tmpfs # Optional: 1GB of memory, reduces SSD/SD Card wear
         target: /tmp/cache
@@ -69,13 +75,14 @@ docker run -d \
   --device /dev/bus/usb:/dev/bus/usb \
   --device /dev/dri/renderD128 \
   -v <path_to_directory_for_media>:/media/frigate \
-  -v <path_to_config_file>:/config/config.yml:ro \
+  -v <path_to_config_directory>:/config:ro \
   -v /etc/localtime:/etc/localtime:ro \
   -e FRIGATE_RTSP_PASSWORD='password' \
   -p 5000:5000 \
   -p 1935:1935 \
-  blakeblackshear/frigate:<specify_version_tag>
+  blakeblackshear/frigate:<arch_image_tag>
 ```
+For M.2 or PCI-e based Coral accelerators, replace `/dev/bus/usb:/dev/bus/usb` with `/dev/apex_0:/dev/apex_0`
 
 ### Calculating shm-size
 
@@ -119,6 +126,8 @@ lxc.cgroup.devices.allow: a
 lxc.cap.drop:
 ```
 
+Note that this assumes that a Coral USB accelerator is used.
+
 ### ESX
 
 For details on running Frigate under ESX, see details [here](https://github.com/blakeblackshear/frigate/issues/305).