luci-app-attendedsysupgrade: Rewrite README.md for spelling, grammar, and clarity

applications/luci-app-attendedsysupgrade/README.md

@@ -1,11 +1,46 @@
 # luci-app-attendedsysupgrade
 
-This app allows firmware upgrades of routers while keeping user installed packages.
-To do so the app sends a request to an *Atttended SysUpgrade server* which will
-respond with a custom image, containing all previously installed packages.
+`luci-app-attendedsysupgrade` is an app for the OpenWrt LuCI web interface
+that facilitates updates and upgrades for both firmware and software packages. 
 
-The process takes per images between 30 seconds and 5 minutes, please be
-patient.
+It appears at `System → Attended Sysupgrade` in the web interface
+where controls and configurations for _when_ it should check for
+firmware upgrades and _where_ it should send build requests are provided.
 
-More information on the backend server and how to host one are available on the
-projects page: https://github.com/openwrt/asu
+Build requests include information about the request system's 
+CPU architecture/target and its currently installed packages. These are sent
+to an **A**ttended **S**ys**U**pgrade server (ASU) which,
+if available, will then respond with an install-ready custom firmware image that
+includes the latest requested firmware and package updates.
+
+By default, this plugin only prompts to send a build request when firmware
+upgrades are detected and the user interactively selects to upgrade.
+
+_Customizable build requests are directly available via the
+`Search for firmware upgrades` button when `Advanced Mode` is active._
+
+Following a successful build request, a prompt appears with information about
+the custom firmware image. The user  may select to install either with
+or without the existing system configuration. 
+There is also an option to download a separate copy
+of that custom image via the web browser. Selecting `Install firmware image`
+closes the prompt and the install proceeds with a system reboot.
+
+ASU servers typically take between 30 seconds and 5 minutes
+to process each build request and prepare a custom image.
+
+> [!NOTE]
+> Following the announcement of a major OpenWrt upgrade, availability of
+> ASU servers may become limited for a few days as target builds are rolled out
+> and servers contend with sharply increased demand.
+
+## Further reading
+If you would like more information about the backend server (and how to
+host one yourself), please visit the [ASU Server repository](https://github.com/openwrt/asu).
+
+Support is available at the official
+[LuCI Attended Sysupgrade support thread](https://forum.openwrt.org/t/luci-attended-sysupgrade-support-thread).
+
+<sub>`luci-app-attendedsysupgrade` is proudly installed in OpenWrt by default
+since the release of 
+[OpenWrt 25.12.0](https://openwrt.org/releases/25.12/notes-25.12.0#integration_of_attended_sysupgrade).</sub>