videoio: doc: add odd width or height limitation for FFMPEG

modules/videoio/include/opencv2/videoio.hpp

@@ -1036,6 +1036,9 @@ public:
     - Most codecs are lossy. If you want lossless video file you need to use a lossless codecs
       (eg. FFMPEG FFV1, Huffman HFYU, Lagarith LAGS, etc...)
     - If FFMPEG is enabled, using `codec=0; fps=0;` you can create an uncompressed (raw) video file.
+    - If FFMPEG is used, we allow frames of odd width or height, but in this case we truncate
+      the rightmost column/the bottom row. Probably, this should be handled more elegantly,
+      but some internal functions inside FFMPEG swscale require even width/height.
     */
     CV_WRAP VideoWriter(const String& filename, int fourcc, double fps,
                 Size frameSize, bool isColor = true);