docs: enhance auto sync documentation with detailed setup, scenarios, and troubleshooting guidance

docs/en/04-sync.md

@@ -7,6 +7,86 @@ description: How to sync your Obsidian notes to Notion using the NotionNext plug
 
 After configuring your Notion database in the plugin settings, you can start syncing your Obsidian notes to Notion.
 
+## Manual Sync
+
 To sync a note, open the note you want to sync and use the "Share to NotionNext" command from the command palette or the note context menu. This will create a new page in your Notion database with the content of your Obsidian note.
 
-You can also set up automatic syncing for specific notes or folders by configuring the plugin settings. This way, any changes you make to your Obsidian notes will be automatically reflected in Notion.
+## Auto Sync
+
+The plugin supports automatic syncing that monitors your notes for changes and automatically syncs them to Notion.
+
+### Enabling Auto Sync
+
+1. Open the plugin settings
+2. Find the "Auto Sync" toggle under General Settings
+3. Enable the toggle
+4. Configure the "Auto Sync Delay" (default: 5 seconds, minimum: 2 seconds)
+
+### How Auto Sync Works
+
+When auto sync is enabled:
+- The plugin monitors markdown files for changes
+- After you stop editing for the configured delay period, auto sync is triggered
+- Only files that have already been synced to Notion (have a NotionID in frontmatter) will be auto-synced
+- If a file is linked to multiple databases, it will sync to all of them automatically
+
+### Auto Sync Scenarios
+
+#### Scenario A: New Document (Not Yet Synced)
+
+```yaml
+---
+title: My New Article
+tags: [blog, tech]
+---
+```
+
+**Behavior:**
+- ✅ Detects no NotionID present
+- ✅ Shows notice: "⚠️ Auto sync skipped: This document has not been synced to Notion, please upload manually first"
+- ✅ No sync operation performed
+- 📝 **Action Required:** Manually sync the document first using the command palette
+
+#### Scenario B: Synced to One Database
+
+```yaml
+---
+title: My Article
+NotionID-blog: abc123
+---
+```
+
+**Behavior:**
+- ✅ Detects 1 NotionID
+- ✅ Automatically syncs to the Blog database
+- ✅ Shows success/failure notification from the upload command
+- 📝 **No Action Required:** Changes are automatically synced
+
+#### Scenario C: Synced to Multiple Databases
+
+```yaml
+---
+title: My Article  
+NotionID-blog: abc123
+NotionID-portfolio: def456
+NotionID-notes: ghi789
+---
+```
+
+**Behavior:**
+- ✅ Detects 3 NotionIDs
+- ✅ Shows notice: "🔄 Auto sync: Syncing to 3 database(s)..."
+- ✅ Syncs to all 3 databases sequentially
+- ✅ Shows individual result notifications for each database
+- 📝 **No Action Required:** Changes are automatically synced to all linked databases
+
+### Auto Sync Best Practices
+
+1. **First Sync Manually**: Always perform the first sync manually to establish the NotionID link
+2. **Configure Delay Appropriately**: Set a longer delay (5-10 seconds) if you make frequent edits
+3. **Monitor Sync Status**: Check the notifications to ensure syncs complete successfully
+4. **Check Logs**: Open the developer console (Ctrl+Shift+I / Cmd+Option+I) to view detailed sync logs
+
+### Troubleshooting
+
+Having issues with auto sync? Check the [Troubleshooting Guide](05-troubleshooting.md) for detailed solutions to common problems.