diff --git a/README.md b/README.md
index 645dadb..64c118f 100644
--- a/README.md
+++ b/README.md
@@ -75,6 +75,15 @@ Use your preferred way to add the `qemush` script to a folder of `PATH`.
 Recommended : copy the script in `/usr/local/bin` to make it effortlessly
 system wide.
 
+### Extra: add `first-free-port` in `PATH`
+
+`first-free-port` is a small C program designed accordingly to the Unix
+philosophy to show in `stdout` the first free (not listening) TCP port
+after `argv[1]`, or `argv[1]` if it is free. You can compile it and add
+it to your `PATH` if you need to allocate ports to protocols like SPICE in
+your launching scripts (example in `qemu/bin/*-spice`). Its source is in
+`src` folder of this repository.
+
 ## Usage
 
 ### Writing a launching script