doc: add docstring for lowlevel

wfassoc-cdylib/src/ffi_types.rs

@@ -22,7 +22,7 @@ pub const INVALID_INDEX: usize = usize::MAX;
 /// However, I don't want to add it as this crate's dependency,
 /// because I don't use anything within it except this type.
 /// So I check Microsoft document, re-define it in there for this crate.
-/// Reference: https://learn.microsoft.com/en-us/windows/win32/winprog/windows-data-types
+/// Reference: <https://learn.microsoft.com/en-us/windows/win32/winprog/windows-data-types>
 pub type HICON = *mut c_void;
 
 /// The invalid value of Win32 HICON handle.