Replace README.txt with README.md

Thanks! Originally, the reason for upper-casing headers was to make headers distinct in txt-format, since it didn't have any other formatting tools.

Since we have ## > h2 formatting available in markdown, we should probably switch to using that, for a more human readable formatting.

So headers could be capitalized, with an initial capital, and not all upper-cased, changing "TRANSLITERATE FILENAMES FOR UPLOADS" to "Transliterate filenames for uploads". The same for "CONTENTS OF THIS FILE", "INTRODUCTION", etc.

I fixing it