Add Note in Readme for "suggested" html5 codecs

Request to add documentation that the "suggested" encoding for html5 is H264 video and AAC audio.

I couldn't get the video to show up in chrome on an mp4 using the mp4 video codec. Audio was mp3 which worked fine, but safari nor firefox would even acknowledge the video.

It wasn't until I ran across a stackexchange question where a guy mentioned reading about "having to use H264 and AAC" for the encoding. I can attest it works. Used TEncoder Video Converter to convert a flv to mp4 using the recommended settings and it worked like a charm. Having this info in the readme would have saved me some time.