cfg: move experimental options to main protocol cfg

sample-lnd.conf

@@ -1306,6 +1306,39 @@
 ; Set to disable blinded route forwarding.
 ; protocol.no-route-blinding=false
 
+; Set to handle messages of a particular type that falls outside of the
+; custom message number range (i.e. 513 is onion messages). Note that you can
+; set this option as many times as you want to support more than one custom
+; message type.
+; Default:
+;   protocol.custom-message=
+; Example:
+;   protocol.custom-message=513
+
+; Specifies feature bits — numbers defined in BOLT 9 — to advertise in the
+; node's init message. Note that you can set this option as many times as you
+; want to support more than one feature bit.
+; Default:
+;   protocol.custom-init=
+; Example:
+;   protocol.custom-init=39
+
+; Specifies custom feature bits — numbers defined in BOLT 9 — to advertise in
+; the node's announcement message. Note that you can set this option as many
+; times as you want to support more than one feature bit.
+; Default:
+;   protocol.custom-nodeann=
+; Example:
+;   protocol.custom-nodeann=39
+
+; Specifies custom feature bits — numbers defined in BOLT 9 — to advertise in
+; the node's invoices. Note that you can set this option as many times as you
+; want to support more than one feature bit.
+; Default:
+;   protocol.custom-invoice=
+; Example:
+;   protocol.custom-invoice=39
+
 [db]
 
 ; The selected database backend. The current default backend is "bolt". lnd