created new example showing echarts usage

examples/echarts/main.py

@@ -0,0 +1,19 @@
+from random import random
+
+from nicegui import ui
+
+option = {"xAxis": {"type": "value"}, "yAxis": {"type": "value"}, "series": [{"data": [[0, 0]], "type": "line"}]}
+
+echarts = ui.echarts(option).style("min-width: 100%").style("min-height: 400px")
+point = 1
+
+
+def update():
+    global point
+    echarts.options["series"][0]["data"].append([point, random()])
+    point = point + 1
+    echarts.update()
+
+
+ui.button("Update", on_click=update)
+ui.run()