bolt04: Add the TLV types for the new payload format

Signed-off-by: Christian Decker <decker.christian@gmail.com>

04-onion-routing.md

@@ -240,7 +240,36 @@ parameters may lead to extraneous routing failure.
 
 ### `tlv_payload` payload format
 
-TBD
+This is a more flexible format, which avoids the redundant `short_channel_id` field for the final node. 
+
+1. tlv: `tlv_payload`
+2. types:
+    1. type: 2 (`amt_to_forward`)
+    2. data:
+        * [`integer`:`amt_to_forward`]
+    1. type: 4 (`outgoing_cltv_value`)
+    2. data:
+        * [`integer`:`outgoing_cltv_value`]
+    1. type: 6 (`short_channel_id`)
+    2. data:
+        * [`8`:`short_channel_id`]
+
+### Requirements
+
+The writer:
+  - MUST include `amt_to_forward` and `outgoing_cltv_value` for every node.
+  - MUST include `short_channel_id` for every non-final node.
+  - MUST NOT include `short_channel_id` for the final node.
+
+The reader:
+  - MUST return an error if `amt_to_forward` or `outgoing_cltv_value` are not present.
+  - MUST return an error if it is not the final node and `short_channel_id` is not present.
+
+The requirements for the contents of these fields are specified [above](#legacy-hop_data-payload-format).
+
+# Accepting and Forwarding a Payment
+
+Once a node has decoded the payload it either accepts the payment locally, or forwards it to the peer indicated as the next hop in the payload.
 
 ## Non-strict Forwarding