docs: add upgrade docs (including breaking changes list)

README.md

@@ -21,6 +21,7 @@ A more advanced, serverless, and free uptime monitoring & status page solution,
   - Customizable Webhook
 - Status page
   - Interactive ping (response time) chart for all types of monitors
+  - Scheduled maintenances alerts & Incident history page
   - Responsive UI that adapts to your system theme
   - Customizable status page
   - Use your own domain with CNAME
@@ -39,6 +40,10 @@ Some screenshots:
 
 Please refer to [Wiki](https://github.com/lyc8503/UptimeFlare/wiki)
 
+## 🚀Upgrade existing deployments
+
+Get the latest features right away with [simple upgrade process](https://github.com/lyc8503/UptimeFlare/wiki/Synchronize-updates-from-upstream)
+
 ## New features (TODOs)
 
 - [x] Specify region for monitors
@@ -63,5 +68,8 @@ Please refer to [Wiki](https://github.com/lyc8503/UptimeFlare/wiki)
 - [ ] Cloudflare D1 database
 - [x] Scheduled maintenances (via IIFE)
 - [ ] Simpler config example
-- [ ] Upcoming maintenances
-- [ ] Universal Webhook upgrade
+- [x] Upcoming maintenances
+- [ ] Universal Webhook upgrade
+- [ ] i18n...? (maybe)
+- [ ] ICMP via proxy?
+- [ ] Add default UA