README.md: Document update checks

Issue: #5

Signed-off-by: Andrew Gunnerson <[email protected]>

README.md

@@ -46,6 +46,10 @@ Custota is installed via a Magisk/KernelSU module so that it can run as a system
 
 7. That's it!
 
+Once the OTA server URL is configured, Custota will automatically check for updates periodically. The checks can be turned off completely or extended to automatically install the updates as well.
+
+To reduce battery usage, the scheduling of the update checks is controlled by Android. They run at most once every 6 hours and will not run at all if the `Require unmetered network` or `Require sufficient battery level` conditions aren't met.
+
 ## OTA server
 
 Custota only requires a basic webserver capable of serving static files and supporting the HTTP `Range` header. Any standard webserver, like Apache, Nginx, or Caddy, will do the trick. For testing, Caddy is very useful because it can serve files from a directory without setting up any config files: