docs: update docs for multi-server support

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/CHEATSHEET.md

@@ -510,6 +510,35 @@ msg.params      # All params list
 msg.tags        # IRCv3 tags dict
 ```
 
+## Multi-Server
+
+```toml
+# config/derp.toml
+[bot]
+prefix = "!"                        # Shared defaults
+plugins_dir = "plugins"
+
+[servers.libera]
+host = "irc.libera.chat"
+port = 6697
+nick = "derp"
+channels = ["#test"]
+
+[servers.oftc]
+host = "irc.oftc.net"
+port = 6697
+nick = "derpbot"
+channels = ["#derp"]
+admins = ["*!~admin@oftc.host"]     # Per-server override
+```
+
+Per-server blocks accept both server keys (host, port, nick, tls, ...)
+and bot overrides (prefix, channels, admins, ...). Unset keys inherit
+from `[bot]`/`[server]` defaults. Legacy `[server]` config still works.
+
+State isolated per server: `data/state-libera.db`, `data/state-oftc.db`.
+Plugins loaded once, shared across all servers.
+
 ## Config Locations
 
 ```