implement table row click callbacks for individual cells

update docs

docs/source/examples/screenshot.md

@@ -0,0 +1,27 @@
+# Screenshot & Save
+
+
+```python
+import pandas as pd
+from lightweight_charts import Chart
+
+
+if __name__ == '__main__':
+    chart = Chart()
+    df = pd.read_csv('ohlcv.csv')
+    chart.set(df)
+    chart.show()
+    
+    img = chart.screenshot()
+    with open('screenshot.png', 'wb') as f:
+        f.write(img)
+```
+
+```{important}
+The `screenshot` command can only be executed after the chart window is open. Therefore, either `block` must equal `False`, the screenshot should be triggered with a callback, or `async_show` should be used. 
+```
+
+```{important}
+This example can only be used with the standard `Chart` object.
+```
+