Add small overview document for every layer

UI/Base/Img.ts

@@ -53,5 +53,17 @@ export default class Img extends BaseUIElement {
         }
         return el;
     }
+    
+    AsMarkdown(): string {
+        if(this._rawSvg === true){
+            console.warn("Converting raw svgs to markdown is not supported");
+            return undefined
+        }
+        let src = this._src
+        if(this._src.startsWith("./")){
+            src = "https://mapcomplete.osm.be/"+src
+        }
+        return "![]("+src+")";
+    }
 }