doc: Prepend 'build/' to binary paths under 'src/' in docs

contrib/tracing/log_p2p_traffic.bt

@@ -5,7 +5,7 @@ BEGIN
   printf("Logging P2P traffic\n")
 }
 
-usdt:./src/bitcoind:net:inbound_message
+usdt:./build/src/bitcoind:net:inbound_message
 {
   $peer_id = (int64) arg0;
   $peer_addr = str(arg1);
@@ -15,7 +15,7 @@ usdt:./src/bitcoind:net:inbound_message
   printf("inbound '%s' msg from peer %d (%s, %s) with %d bytes\n", $msg_type, $peer_id, $peer_type, $peer_addr, $msg_len);
 }
 
-usdt:./src/bitcoind:net:outbound_message
+usdt:./build/src/bitcoind:net:outbound_message
 {
   $peer_id = (int64) arg0;
   $peer_addr = str(arg1);