doc: add tutorials as Doxygen examples

doc/tutorial1.dox

@@ -11,20 +11,7 @@ environment.
 
 Let get started with the simplest application.
 
-\code{.c}
-#include <pipewire/pipewire.h>
-
-int main(int argc, char *argv[])
-{
-	pw_init(&argc, &argv);
-
-	fprintf(stdout, "Compiled with libpipewire %s\n"
-                        "Linked with libpipewire %s\n",
-                                pw_get_headers_version(),
-                                pw_get_library_version());
-	return 0;
-}
-\endcode
+\snippet tutorial1.c code
 
 Before you can use any PipeWire functions, you need to call `pw_init()`.