f add backwards compat notes

Author: TheBlueMatt

CHANGELOG.md

@@ -49,6 +49,14 @@ the old mempool/low/medium/high priorities are as follows:
    prior to reconnection can be sent after reconnection. This could result in
    undefined channel state and force-closes (#2663).
 
+## Backwards Compatibility
+
+ * Creating a blinded path to receive a payment then downgrading to LDK prior to
+   0.0.117 may result in failure to receive the payment (#2413).
+ * Calling `ChannelManager::pay_for_offer` or
+   `ChannelManager::create_refund_builder` may prevent downgrading to LDK prior
+   to 0.0.118 until the payment times out and has been removed (#2039).
+
 ## Node Compatibility
  * LDK now sends a bogus `channel_reestablish` message to peers when they ask to
    resume an unknown channel. This should cause LND nodes to force-close and