update readme

README.md

@@ -2,7 +2,7 @@
 
 [![CD](https://github.com/nolze/tiny-wifi-analyzer/workflows/CD/badge.svg)](https://github.com/nolze/tiny-wifi-analyzer/actions?query=workflow%3ACD)
 
-A ***tiny*** Wi-Fi channels & strengths analyzer for macOS.
+Simple, open-source Wi-Fi channel and strength analyzer for macOS.
 Made with PyObjC, pywebview, ApexCharts, PyInstaller.
 
 ![screenshot](assets/screenshot.png)
@@ -13,7 +13,17 @@ Made with PyObjC, pywebview, ApexCharts, PyInstaller.
 
 ## Download
 
-* [Visit the latest release](https://github.com/nolze/tiny-wifi-analyzer/releases/latest/)
+[Visit the latest release](https://github.com/nolze/tiny-wifi-analyzer/releases/latest/)
+
+### Important note
+
+Since the app is not signed, you need to follow the steps below to run it.
+
+(1) **right-click on the icon**,\
+(2) select "Open" from the context menu,\
+(3) and select "OK" in the dialog.
+
+<img src="https://user-images.githubusercontent.com/291323/179491872-3a9e6c4c-b8cb-4081-ac88-bd1817d6ba4d.png" width="300px">
 
 ## Todos