Update docs

src/core/filesystem/apk_filesystem.h

@@ -17,6 +17,8 @@ namespace crown
 {
 /// Access files on Android's assets folder.
 /// The assets folder is read-only and all the paths are relative.
+///
+/// @ingroup Filesystem
 class ApkFilesystem : public Filesystem
 {
 	Allocator* _allocator;