Move documentation from binary pdf files to plain text files

[dstansby]

I noticed some of the (super useful!) documetation in the root directory of the repository is in .pdf files. I wanted to suggest moving from a .pdf format to another format that isn't a binary file, like MarkDown or ReStructuredText. That way it would be possible to version control the text properley and see what's changed as the documentation is updated between new Kamodo versions.