doc: add tutorials as Doxygen examples

doc/tutorial1.c

@@ -0,0 +1,19 @@
+/*
+  [title]
+  \ref page_tutorial1
+  [title]
+ */
+/* [code] */
+#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;
+}
+/* [code] */