fix: Add example to README

README.md

@@ -7,3 +7,45 @@
 ## Build
 
 `dotnet run Bundle`
+
+## Example usage
+
+```fsharp
+let geoJson = """
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "geometry": {
+        "type": "Point",
+        "coordinates": [102.0, 0.5]
+      },
+      "properties": {
+        "prop0": "value0"
+      }
+    },
+    {
+      "type": "Feature",
+      "geometry": {
+        "type": "Polygon",
+        "coordinates": [
+          [
+            [100.0, 0.0], [101.0, 0.0], [101.0, 1.0],
+            [100.0, 1.0], [100.0, 0.0]
+          ]
+        ]
+      }
+    }
+  ]
+}
+"""
+
+let readJson () =
+    let result = FeatureCollection.Decode geoJson
+    match result with
+    | Ok json -> printfn $"%A{json.Features}"
+    | Error e -> printfn $"decode failed: {e}"
+
+let encodeJson (json: FeatureCollection) = json.Encode ()
+```