Improve cache description. Suggested by Gernot.Reisinger@omnino.at.
diff --git a/include/freetype/ftcache.h b/include/freetype/ftcache.h
index a9e1237..fe8664d 100644
--- a/include/freetype/ftcache.h
+++ b/include/freetype/ftcache.h
@@ -56,9 +56,12 @@ FT_BEGIN_HEADER
* interpret them in any way.
*
* Second, the cache calls, only when needed, a client-provided function
- * to convert a @FTC_FaceID into a new @FT_Face object. The latter is
+ * to convert an @FTC_FaceID into a new @FT_Face object. The latter is
* then completely managed by the cache, including its termination
- * through @FT_Done_Face.
+ * through @FT_Done_Face. To monitor termination of face objects, the
+ * finalizer callback in the `generic' field of the @FT_Face object can
+ * be used, which might also be used to store the @FTC_FaceID of the
+ * face.
*
* Clients are free to map face IDs to anything else. The most simple
* usage is to associate them to a (pathname,face_index) pair that is