docs: warn against running a second inventory manager

README.md

@@ -18,6 +18,55 @@ The following are switched per-world:
 3. Done!
 4. (Optional) If you would prefer to have achievements not broadcasted in your server chat when players change worlds, run the command `/gamerule announceAdvancements false` in-game, or in your server console by removing the "/" symbol. 
 
+## Do not run two inventory managers
+
+InvSwitcher must be the only plugin managing per-world inventories. Running it alongside
+Multiverse-Inventories, PerWorldInventory, MultiInv or similar makes both plugins save and restore
+the player on every world change, and they overwrite each other's data.
+
+The symptom is disappearing items: pick up an item on your island, go to the lobby, come back, and
+the island inventory is empty. Nothing appears in the console, because neither plugin is failing —
+each is faithfully saving a player state the other has already rewritten. The InvSwitcher version
+makes no difference, so if you are seeing this, look for a second inventory plugin first.
+
+### Multiverse-Inventories
+
+Two things commonly mislead admins:
+
+* **Leaving the BentoBox worlds out of every inventory group does not help.** Groups control which
+  worlds *share* an inventory, not which worlds Multiverse-Inventories handles. It still writes a
+  per-world profile for a world that is in no group.
+* **`/mv remove <world>` does not help either.** Multiverse-Core re-registers BentoBox worlds as
+  they are created, so the removal is undone on the next restart. `auto-import-3rd-party-worlds:
+  false` does not prevent it — that only suppresses the import sweep run when Multiverse-Core
+  starts, which is before BentoBox has created its worlds.
+
+Multiverse-Inventories has no config option to ignore a world, but it does have a bypass
+permission. Enable it in the Multiverse-Inventories `config.yml` (it ships as `false`):
+
+```yml
+share-handling:
+  enable-bypass-permissions: true
+```
+
+Then grant `mvinv.bypass.world.<world>` for each BentoBox world — including its nether and end — to
+every player. With LuckPerms:
+
+```
+lp group default permission set mvinv.bypass.world.bskyblock_world true
+lp group default permission set mvinv.bypass.world.bskyblock_world_nether true
+lp group default permission set mvinv.bypass.world.bskyblock_world_the_end true
+```
+
+Setting the nodes on a group every player inherits (such as `default`) covers new players
+automatically. Repeat for each game mode world you run.
+
+**Operators do not get this permission automatically** — it has to be granted explicitly. Testing
+as an op without it looks exactly like the fix not working.
+
+Use one node per world. Avoid `mvinv.bypass.world.*`, which switches Multiverse-Inventories off for
+every world, including the ones you still want it to manage.
+
 ## Config.yml
 
 The config allows to define which worlds that InvSwitcher should operate, and what aspects should be kept separate.