Docs: Added a guide on integrating Discord. (#15156)

### What problem does this PR solve?

How to ingest messages from your Discord server.

### Type of change

- [x] Documentation Update

docs/guides/dataset/add_data_source/add_discord.md

@@ -0,0 +1,58 @@
+---
+sidebar_position: 7
+slug: /add_discord
+sidebar_custom_props: {
+  categoryIcon: SiGoogledrive
+}
+---
+
+# Add Discord
+
+Integrate Discord as a data source.
+
+---
+
+This guide outlines how to ingest messages from your Discord servers into RAGFlow by setting up a dedicated bot.
+
+## Prerequisites
+
+- Administrative privileges for the target Discord server.
+- Permissions to add data sources within your RAGFlow environment.
+
+## Setting up a Discord bot
+
+You need a bot application to access and read messages from your server securely.
+
+- Go to the Discord Developer Portal.
+- Select "New Application" and assign it a descriptive name.
+- Navigate to the "Bot" section in the left menu and add a new bot.
+- Scroll down to the "Privileged Gateway Intents" section and toggle on "Message Content Intent" so the application can extract message text.
+- Click "Reset Token" to generate your bot token. Copy this token immediately and store it safely.
+
+## Invite the bot to your server
+
+The bot must be authorized to view the specific channels you intend to sync.
+
+- In the Developer Portal, open the "OAuth2" menu and select "URL Generator".
+- Check the `bot` scope.
+- In the permission list, select "View Channels" and "Read Message History".
+- Copy the resulting URL generated at the bottom of the screen.
+- Open this URL in your browser, select your desired server from the dropdown, and approve the authorization prompt.
+
+## Configure the connection in RAGFlow
+
+With the bot active in your server, you can finalize the integration inside RAGFlow.
+
+- Open RAGFlow and access the data sources configuration module.
+- Choose "Discord" from the list of supported external platforms.
+- Paste your saved bot token into the designated input field.
+- Configure any specific channels or indexing preferences as required by the interface.
+- Save your settings to establish the connection.
+- Attach this newly created Discord data source to your target dataset to begin syncing your conversations.
+
+### Link to a dataset
+
+1. Navigate to the **Dataset** tab.
+2. Select or create the target Dataset.
+3. Navigate to the Dataset's **Configuration** page and select **Link data source**.
+4. Choose the previously created Discord connector in the popup window.