docs: polish rtorrent URL path documentation to exact specifications

- Update .env.sample RTORRENT_INSTANCES section with exact comment format
- Update README.md rTorrent table row with specific endpoint note
- Add explicit "No path is automatically appended" statement in README
- RTorrentClient.js already uses exact URL from config (no changes needed)

.env.sample

@@ -95,24 +95,15 @@ QBITTORRENT_INSTANCES=[{"name":"main","url":"https://qbittorrent.example.com","u
 # QBITTORRENT_PASSWORD=your-password
 
 # =============================================================================
-# RTORRENT INSTANCES (JSON Array Format)
-# Add one or more rTorrent instances as a single-line JSON array
-# Uses username/password authentication (optional)
-# Format: [{"name":"instance-name","url":"https://...","username":"...","password":"..."}]
-# IMPORTANT: XML-RPC endpoint must be included in the url field (no automatic appending).
-# Standard installs use /RPC2. Some providers (e.g. whatbox.ca) use /xmlrpc. Other
-# installations may use a custom path. Always supply the complete RPC endpoint.
-# Examples:
-#   Standard: http://rtorrent.local:8080/RPC2
-#   whatbox.ca: https://user.whatbox.ca/xmlrpc
-#   Custom: https://example.com/custom/rpc/path
-# =============================================================================
-# RTORRENT_INSTANCES=[{"name":"main","url":"http://rtorrent.example.com/RPC2","username":"rtorrent","password":"rtorrent"}]
-
-# Legacy single-instance format (optional - still supported)
-# RTORRENT_URL=http://rtorrent.example.com/RPC2
-# RTORRENT_USERNAME=rtorrent
-# RTORRENT_PASSWORD=rtorrent
+# RTORRENT_INSTANCES (JSON Array)
+# The url MUST include the full XML-RPC endpoint path.
+# Standard/self-hosted installs: .../RPC2
+# whatbox.ca users: .../xmlrpc
+# Other installations may use different custom paths.
+# Example:
+RTORRENT_INSTANCES=[{"name":"main","url":"http://rtorrent.local:8080/RPC2","username":"rtorrent","password":"rtorrent"}]
+# For whatbox.ca:
+# RTORRENT_INSTANCES=[{"name":"whatbox","url":"https://user.whatbox.ca/xmlrpc","username":"user","password":"pass"}]
 
 # =============================================================================
 # SONARR INSTANCES (JSON Array Format)