Slight fixes to make FreeBSD compilation easier

Readme-BSD.txt

@@ -0,0 +1,31 @@
+PCem v14 BSD supplement
+
+
+You will need the following libraries :
+
+SDL2
+wxWidgets 3.x
+OpenAL
+
+and their dependencies.
+
+Open a terminal window, navigate to the PCem directory then enter
+
+./configure --enable-release-build
+gmake
+
+then ./pcem to run.
+
+The BSD version stores BIOS ROM images, configuration files, and other data in ~/.pcem
+
+configure options are :
+  --enable-release-build : Generate release build. Recommended for regular use.
+  --enable-debug         : Compile with debugging enabled.
+  --enable-networking    : Build with networking support.
+  --enable-alsa          : Build with support for MIDI output through ALSA. Requires libasound.
+
+
+The menu is a pop-up menu in the BSD port. Right-click on the main window when mouse is not
+captured.
+
+CD-ROM support currently only accesses /dev/cdrom. It has not been heavily tested.