Update readme

Author: tulir

README.md

@@ -1,5 +1,7 @@
 # mac-registration-provider
-A small service that generates iMessage registration data on a Mac. If you do not have access to Beeper Cloud, you can use this to generate a iMessage Registration Code and use it in Beeper Mini. 
+A small service that generates iMessage registration data on a Mac. If you do
+not have access to Beeper Cloud, you can use this to generate an iMessage
+registration code and use it in Beeper Mini.
 
 ## Supported MacOS versions
 The tool is currently quite hacky, so it only works on specific versions of macOS.
@@ -11,17 +13,21 @@ On unsupported versions, it will tell you that it's unsupported and exit.
 A future version may work in less hacky ways to support more OS versions.
 
 ## Usage
-1. On your Mac, download the latest `mac-registration-provider` file from the latest [release](https://github.com/beeper/mac-registration-provider/releases)
-![CleanShot 2023-12-21 at 14 32 42@2x](https://github.com/beeper/mac-registration-provider/assets/1048265/4a419ae1-8996-4af4-876e-5723db088816)
-2. Open Terminal app (⌘+space -> Terminal), type `cd Downloads`, hit enter
-3. type `chmod +x mac-registration-provider`, hit enter
-4. Type `./mac-registration-provider`, hit enter
+1. On your Mac, download the latest `mac-registration-provider` file from the
+   latest [release](https://github.com/beeper/mac-registration-provider/releases)
 
+   ![screenshot](https://github.com/beeper/mac-registration-provider/assets/1048265/4a419ae1-8996-4af4-876e-5723db088816)
+2. Open Terminal app (<kbd>⌘</kbd> + <kbd>space</kbd> -> Terminal), type `cd Downloads`, hit enter
+3. Type `chmod +x mac-registration-provider`, hit enter
+4. Type `./mac-registration-provider`, hit enter
 
 ## Future improvements
 If anyone wants to package this into an app that lives in your dock and runs at startup, we'd appreciate it!
 
-## Optional parameters:
+## Modes of operation
+The service has three different modes of operation, and various flags associated
+with each mode. Only one mode can be used at a time. The only mode that works
+with Beeper is Relay, which is the default.
 
 * Relay (default) - connect to a websocket and return registration data when the server requests it.
   * `-relay-server` Use a different relay server (defaults to `https://registration-relay.beeper.com`).