Adds build instructions and references the special SDL key combinations.

BUILD.txt

@@ -0,0 +1,30 @@
+Linux, BSD
+==========
+
+Prerequisites are SDL 2, ZLib and OpenGL (or Mesa), and SConstruct for the provided build script. OpenGL 3.2 or better is required at runtime.
+
+Build:
+
+	cd OSBindings/SDL
+	scons
+
+Optionally:
+
+	cp clksignal /usr/bin
+
+To launch:
+
+	clksignal file
+
+Setting up clksignal as the associated program for supported file types in your favoured filesystem browser is recommended; it has no file navigation abilities of its own.
+
+Some emulated systems require the provision of original machine ROMs. These are not included and may be located in either /usr/local/share/CLK/ or /usr/share/CLK/. You will be prompted for them if they are found to be missing. The structure should mirror that under OSBindings in the source archive; see the readme.txt in each folder to determine the proper files and names ahead of time.
+
+macOS
+=====
+
+There are no prerequisites beyond the normal system libraries; the macOS build is a native Cocoa application.
+
+Build: open the Xcode project in OSBindings/Mac and press command+b.
+
+Machine ROMs are intended to be built into the application bundle; populate the dummy folders below ROMImages before building.

OSBindings/SDL/main.cpp

@@ -214,6 +214,7 @@ int main(int argc, char *argv[]) {
 	// Print a help message if requested.
 	if(arguments.selections.find("help") != arguments.selections.end() || arguments.selections.find("h") != arguments.selections.end()) {
 		std::cout << "Usage: " << final_path_component(argv[0]) << " [file] [OPTIONS]" << std::endl;
+		std::cout << "Use alt+enter to toggle full screen display. Use control+shift+V to paste text." << std::endl;
 		std::cout << "Required machine type and configuration is determined from the file. Machines with further options:" << std::endl << std::endl;
 
 		auto all_options = Machine::AllOptionsByMachineName();