Add homes_left placeholder reference

Author: vLuckyyy

docs/eternalcore/placeholders.md

@@ -13,3 +13,4 @@ If you have a suggestion to add new placeholders, please create an issue on [Git
 - `%eternalcore_homes_owned%` - 🏠 Houses owned by the player
 - `%eternalcore_homes_count%` - 📊 Number of houses owned by the player
 - `%eternalcore_homes_limit%` - 📅 Limit of the maximum houses for a specific player
+- `%eternalcore_homes_left%` - ⬅️ Number of left houses that the player can create