Add note about BusyBox installation

README.md

@@ -31,6 +31,10 @@ Then to access a small unix environment:
     busybox sh -l
 
 This will expose the rest of busybox's commands without further action.
+However, the unix environment will not be available to other tools such
+as `make` without "installing" BusyBox into the `bin/` directory:
+
+    busybox --install
 
 ## Notes