Add documentation section

Explain how to configure bitcoind to ensure you'll be able to use CPFP without
hitting unconfirmed transaction chains mempool limits.

README.md

@@ -148,6 +148,22 @@ If you want to use a different wallet from the default one, you must set `eclair
 Eclair will return BTC from closed channels to the wallet configured.
 Any BTC found in the wallet can be used to fund the channels you choose to open.
 
+We also recommend tweaking the following parameters in `bitcoin.conf`:
+
+```conf
+# This parameter ensures that your wallet will not create chains of unconfirmed
+# transactions that would be rejected by other nodes.
+walletrejectlongchains=1
+# The following parameters set the maximum length of chains of unconfirmed
+# transactions to 20 instead of the default value of 25.
+limitancestorcount=20
+limitdescendantcount=20
+```
+
+Setting these parameters lets you unblock long chains of unconfirmed channel funding transactions by using child-pays-for-parent (CPFP) to make them confirm.
+
+With the default `bitcoind` parameters, if your node created a chain of 25 unconfirmed funding transactions with a low-feerate, you wouldn't be able to use CPFP to raise their fees because your CPFP transaction would likely be rejected by the rest of the network.
+
 ### Java Environment Variables
 
 Some advanced parameters can be changed with java environment variables. Most users won't need this and can skip this section.
@@ -278,9 +294,14 @@ so you can easily run your Bitcoin node on both mainnet and testnet. For example
 ```conf
 server=1
 txindex=1
+
 addresstype=bech32
 changetype=bech32
 
+walletrejectlongchains=1
+limitancestorcount=20
+limitdescendantcount=20
+
 [main]
 rpcuser=<your-mainnet-rpc-user-here>
 rpcpassword=<your-mainnet-rpc-password-here>

docs/release-notes/eclair-vnext.md

@@ -40,6 +40,7 @@ All this data is signed and encrypted so that it can not be read or forged by th
 - `channel-opened` websocket event was updated to contain the final `channel_id` and be published when a channel is ready to process payments (#2567)
 - `getsentinfo` can now be used with `--offer` to list payments sent to a specific offer.
 - `listreceivedpayments` lists payments received by your node (#2607)
+- `cpfpbumpfees` can be used to unblock chains of unconfirmed transactions by creating a child transaction that pays a high fee (#1783)
 
 ### Miscellaneous improvements and bug fixes