✨ Add Trello Trigger node docs

docs/nodes/nodes-library/trigger-nodes/TrelloTrigger/README.md

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+---
+permalink: /nodes/n8n-nodes-base.trelloTrigger
+---
+
+# Trello Trigger
+
+[Trello](https://trello.com/) is a web-based Kanban-style list-making application which is a subsidiary of Atlassian. Users can create their task boards with different columns and move the tasks between them. 
+
+::: tip 🔑 Credentials
+You can find authentication information for this node [here](../../../credentials/Trello/README.md).
+:::
+
+
+## Example Usage
+
+This workflow allows you to receive updates for changes in the specified list in Trello. You can also find the [workflow](https://n8n.io/workflows/491) on the website. This example usage workflow would use the following node.
+- [Trello Trigger]()
+
+The final workflow should look like the following image.
+
+![A workflow with the Trello Trigger node](./workflow.png)
+
+
+### 1. Trello Trigger node
+
+1. First of all, you'll have to enter credentials for the Trello Trigger node. You can find out how to do that [here](../../../credentials/Trello/README.md).
+2. Enter the ID of the list in the *Model ID* field. You can find instructions on how to do that in the FAQs below.
+3. Click on *Execute Node* to run the workflow.
+
+
+## FAQs
+
+### How do I find the Model ID?
+
+For this specific example, the List ID would be the Model ID.
+
+1. Open the Trello board that contains the list.
+2. If the list doesn't have any cards, add a card to the list.
+3. Open the card, add '.json' at the end of the URL, and press enter.
+4. In the JSON file, you will see a field called `idList`.
+5. Copy `idList`and paste it in the *Model ID* field in n8n.
+
+
+### What is the Model ID?
+
+It is the ID of any model in Trello. Depending on the use-case, it could be the User ID, List ID, and so on.