Add file support description

[Jesper-Hustad]

There has been feedback that the project lacks description of supported file types.
Currently this is images such as jpg, jpeg, png, and gif

This can be added in the html under "Drop or paste here" in small, but readable text.

[kyle-christian]

I can do this :)

edit: finished!

[kevinmilleryo]

I was working on this as well but Kyle beat me to it! I added a pull request anyway. Thanks!

[Jesper-Hustad]

Good job! I will be merging @kyle-christian's PR as they where first, but @kevinmilleryo works great as well.

Btw, how did you find this repo? Hacktoberfest hasn't officially begun yet, and this project is still pretty new.
Just curious, thanks again for the help :)

[kevinmilleryo]

Jesper, I saw it on goodfirstissues.com. I'll keep an eye out for any other issues on this project I think I may be able to handle.