describe more detail about window modes in README (#15)

README.md

@@ -20,8 +20,8 @@ Features:
 Mastodon is an open source project. So if you want to make a new UI, you can just fork the project,
 implement your favorite UI and host it on your place. Then you can participate Mastodon networks from it.
 
-However, Mastodon is a web application. So we can't go out from a browser. So this small tool
-provides a way to do it.
+However, Mastodon is a web application. So we can't go out from a browser. This small tool provides
+the ability to Mastodon page in desktop application window out of browser.
 
 ## Installation
 
@@ -52,6 +52,17 @@ Some shortcuts are available by default (please see below 'Customization' sectio
 
 Supported platforms are macOS (confirmed with 10.12), Linux (hopefully) and Windows (confirmed with Windows 8.1).
 
+There are two window modes 'menubar mode' and 'normal window mode' in this app. You can switch
+them with `"normal_window"` option (please see below 'Customization' section for how to configure it).
+
+- **menubar mode**: Window is attached to menubar. You can toggle the window by clicking menubar icon or typing hot key.
+Advantage of this mode is that app does not fill any workspace. You can see your timeline on demand anytime.
+- **normal window mode**: App starts with a normal window like a separated browser window. You can put/resize window
+as you like in your workspace.
+
+In both modes, app remembers the size and location of its window. So you need to specify window size
+(or location in normal window mode) only once.
+
 ## Customization
 
 Mstdn can be customized with JSON config file at `{app dir}/config.json`