Update README

README

@@ -3,8 +3,10 @@
 This is a clone (ish) of the classic game Asteroids, written in C23
 for Linux.  To build the program, you'll need the Linux headers, a
 C23-compatible compiler and libdrm, along with its headers.  There is
-a build script that uses GCC; simply running this (`./build.sh`) is
-likely to work on many systems.
+a build script that uses GCC; simply running this (./build.sh) is
+likely to work on many systems.  However, you will likely need to
+adjust the input and video devices used (in input.c and renderer.c
+respectively) to match your system.
 
 The game directly uses Linux DRM, so it doesn't play nice with X,
 display managers etc.  You'll likely want to change to a virtual TTY