Add info about notifications to README

samples/notify_send_sample.lua

@@ -0,0 +1,35 @@
+function on_resume()
+    ui:show_lines{
+        "Show notify",
+        "Update notify",
+        "Cancel notify",
+    }
+end
+
+function on_click(idx)
+    if idx == 1 then
+        system:show_notify{
+            message = "Just message",
+            silent = true,
+            action1 = "cancel",
+        }
+    elseif idx == 2 then
+        system:show_notify{
+            message = "Message updated",
+            silent = true,
+            action1 = "cancel",
+            action2 = "action #2",
+            action3 = "action #3",
+        }
+    else
+        system:cancel_notify()
+    end
+end
+
+function on_notify_action(idx, action)
+    ui:show_toast("action: "..idx..": "..action)
+
+    if action == "cancel" then
+        system:cancel_notify()
+    end
+end