Add missing migration info to docs.

Author: h2zero

docs/1.x_to2.x_migration_guide.md

@@ -65,7 +65,8 @@ This returns a pointer to `const ble_addr_t` instead of a pointer to the address
 ## Server
 - `NimBLEServer::disconnect` now returns `bool`, true = success,  instead of `int` to be consistent with the rest of the library.
 - `NimBLEServerCallbacks::onMTUChanged` renamed to `NimBLEServerCallbacks::onMTUChange` to be consistent with the client callback.
-- `NimBLEServer::getPeerIDInfo` renamed to `NimBLEServer::getPeerInfoByHandle` to better describe it's use.  
+- `NimBLEServer::getPeerIDInfo` renamed to `NimBLEServer::getPeerInfoByHandle` to better describe it's use.
+- Advertising is no longer automatically restarted when a peer disconnects, to re-enable this feature either call `NimBLEServer::advertiseOnDisconnect(true);` after creating the server or manually restart advertising in the `onDisconnect` callback.   
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 ### Services