added documentation for TileJSON discovery

docs/TileJSON-Discovery.md

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+# Adding TileJSON Map Services
+
+This guide explains how to add map tiles from a TileJSON server (like mbtileserver) to ODIN.
+
+## What is TileJSON?
+
+TileJSON is a format for describing map tile services. Servers like [mbtileserver](https://github.com/consbio/mbtileserver) can serve `.mbtiles` files and provide a list of available map layers that ODIN can discover and display.
+
+## Step-by-Step Guide
+
+### Step 1: Create a New Tile Service
+
+1. Press `Ctrl+N` followed by `T` to create a new tile service
+2. A new tile service appears in the sidebar and its properties panel opens
+
+### Step 2: Enter the Server URL
+
+1. In the **URL** field, enter the address of your TileJSON server
+   - Example: `http://localhost:8000/services`
+2. Press `Tab` or click outside the field to confirm
+
+### Step 3: Select Map Layers
+
+1. ODIN automatically detects the available tilesets and displays them as a list
+2. Each tileset has a checkbox next to its name
+3. Click the checkbox next to the tilesets you want to add
+
+### Step 4: View in Background Maps
+
+1. The selected tilesets now appear in the **Background Maps** control
+2. To open Background Maps, click on the tile preset in the sidebar (or use `Ctrl+Shift+T`)
+3. Here you can:
+   - **Toggle visibility**: Click the eye icon to show/hide a map layer
+   - **Adjust opacity**: Click the opacity icon and use the slider
+   - **Change order**: Drag layers up or down to change their stacking order
+
+## Tips
+
+- You can select multiple tilesets from the same server
+- New layers are hidden by default - click the eye icon to make them visible
+- The zoom levels are automatically configured based on the tileset's settings
+
+## Troubleshooting
+
+| Problem | Solution |
+|---------|----------|
+| No tilesets appear | Check that the server URL is correct and the server is running |
+| Tiles don't load | Verify the server is accessible from your computer |
+| Layer has no name | The server may not provide names - the tileset will still work |
+
+## Example Setup with mbtileserver
+
+1. Install mbtileserver: `go install github.com/consbio/mbtileserver@latest`
+2. Place your `.mbtiles` files in a folder
+3. Start the server: `mbtileserver --dir /path/to/tiles`
+4. In ODIN, enter: `http://localhost:8000/services`