rfq: improve BuyOrder doc

rfq/manager.go

@@ -688,7 +688,25 @@ func (m *Manager) UpsertAssetBuyOffer(offer BuyOffer) error {
 	return nil
 }
 
-// BuyOrder is a struct that represents a buy order.
+// BuyOrder instructs the RFQ (Request For Quote) system to request a quote from
+// a peer for the acquisition of an asset.
+//
+// The normal use of a buy order is as follows:
+//  1. Alice, operating a wallet node, wants to receive a Tap asset as payment
+//     by issuing a Lightning invoice.
+//  2. Alice has an asset channel established with Bob's edge node.
+//  3. Before issuing the invoice, Alice needs to agree on an exchange rate with
+//     Bob, who will facilitate the asset transfer.
+//  4. To obtain the best exchange rate, Alice creates a buy order specifying
+//     the desired asset.
+//  5. Alice's RFQ subsystem processes the buy order and sends buy requests to
+//     relevant peers to find the best rate. In this example, Bob is the only
+//     available peer.
+//  6. Once Bob provides a satisfactory quote, Alice accepts it.
+//  7. Alice issues the Lightning invoice, which Charlie will pay.
+//  8. Instead of paying Alice directly, Charlie pays Bob.
+//  9. Bob then forwards the agreed amount of the Tap asset to Alice over their
+//     asset channel.
 type BuyOrder struct {
 	// AssetSpecifier is the asset that the buyer is interested in.
 	AssetSpecifier asset.Specifier