diff --git a/README.md b/README.md
index a0a473e..cbd02a6 100644
--- a/README.md
+++ b/README.md
@@ -45,6 +45,9 @@ So for example the ui_vt100.c supports all platforms where vt100 escape codes ar
 When implementing a new ui, you can start from `ui_stub.c`.
 This "ui" is just the bare minimum to let the rest of the code work.
 
+## `commandline.h`
+The `commandline.h` file has the function that handles command-line argument parsing.
+
 ## `logic.h`
 The `logic.h` file has the types used in `logic.c` and the functions it exposes.