moved outline to text files

I have moved the contents of the pdf v.2 to text files because they are easier to track in version control, and make it possible to edit, also have separated out the text into the README and outline documents.

In addition to the timeline table, I am happy to show how we can use the [issues](https://github.com/soil-metamodel/Litter-decomp-mapping/issues) and [milestones](https://github.com/soil-metamodel/Litter-decomp-mapping/milestones) features in GitHub .