update doc comments

Author: colbyn

src/api.rs

@@ -13,6 +13,7 @@
 //! Notes:
 //! * **Be advised, exported API yet not stable. Prefer directly using symbols from the `ffmpeg_dev::sys` module over this one.**
 //! * Also note that this will be be incomplete.
+//! * Things have improved a bit since removing autogenerated layout tests from `ffmpeg_dev::sys`.
 
 // pub mod avcodec;
 // pub mod avdevice;