sample-lnd: add anchors to sample config

sample-lnd.conf

@@ -337,6 +337,11 @@
 ; automatically. [experimental]
 ; keysend-hold-time=true
 
+; If set, lnd will use anchor channels by default if the remote channel party
+; supports them. Note that lnd will require 1 UTXO to be reserved for this
+; channel type if it is enabled.
+; protocol.anchors=true
+
 ; If true, we'll attempt to garbage collect canceled invoices upon start.
 ; gc-canceled-invoices-on-startup=true