docs(zigbee2mqtt): Add Installation-Guide (#17290)

Added installation docu/hints

**Description**
Added Documentation for zigbee2mqtt module (installation guides).

⚒️ Fixes  # 
none, just copied from Discord channel

**⚙️ Type of change**

- [x] ⚙️ Feature/App addition
- [ ] 🪛 Bugfix
- [ ] ⚠️ Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] 🔃 Refactor of current code

**🧪 How Has This Been Tested?**

Not tested since only docu. Since this is my first commit, someone
should shortly check the changes manually.

**📃 Notes:**
n/a

**✔️ Checklist:**

- [x] ⚖️ My code follows the style guidelines of this project
- [ ] (no code!) 👀 I have performed a self-review of my own code
- [ ] #️⃣ I have commented my code, particularly in hard-to-understand
areas
- [x] 📄 I have made corresponding changes to the documentation
- [ ] ⚠️ My changes generate no new warnings
- [ ] 🧪 I have added tests to this description that prove my fix is
effective or that my feature works
- [ ] ⬆️ I increased versions for any altered app according to semantic
versioning

**➕ App addition**

If this PR is an app addition please make sure you have done the
following.

- [ ] 🪞 I have opened a PR on
[truecharts/containers](https://github.com/truecharts/containers) adding
the container to TrueCharts mirror repo.
- [ ] 🖼️ I have added an icon in the Chart's root directory called
`icon.png`

---

_Please don't blindly check all the boxes. Read them and only check
those that apply.
Those checkboxes are there for the reviewer to see what is this all
about and
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---------

Signed-off-by: StevenMcElligott <89483932+StevenMcElligott@users.noreply.github.com>
Signed-off-by: Stavros Kois <47820033+stavros-k@users.noreply.github.com>
Co-authored-by: StevenMcElligott <89483932+StevenMcElligott@users.noreply.github.com>
Co-authored-by: Stavros Kois <47820033+stavros-k@users.noreply.github.com>

charts/stable/zigbee2mqtt/docs/installation.md

@@ -0,0 +1,30 @@
+---
+title: Installation Guide
+---
+
+## TrueNAS SCALE Installation Hints
+
+Here's an example of a default installation of zigbee2mqtt. Pay particular attention to the section "Configure Mount USB Devices" to configure the USB adapter to your container as those two paths should match. 
+
+### Application Configuration
+
+Enter `MQTT User`, `MQTT Password` if necessary, as this will override the specific value of config file. Leave empty if you plan to use custom config or you don't have set a user on your MQTT broker.
+
+For `MQTT Server` Internal DNS Cluster IP can be used (default) of `mqtt://mosquitto.ix-mosquitto.svc.cluster.local` or you can use the external IP.
+
+![config1](images/config1.png)
+![config1](images/config1.png)
+![config2](images/config2.png)
+![config3](images/config3.png)
+![config4](images/config4.png)
+![config5](images/config5.png)
+
+### Mount USB Devices
+
+Make sure `Enable the Storage is Checked` and enter your USB device by ID as per below, in this example we use `/dev/serial/by-id/usb-ithead_SONOFF`
+
+![config6](images/config6.png)
+
+This guide should prevent one of the following error messages:
+![error message 1](images/error_log1.png)
+![error message 2](images/error_log2.png)