Update of the README.md with technical info #75

[nicolasdesaintjorre]

New version of the README.md with more information and a complete how to install it.

[swhume]

Overall, it looks great and has the right kind of technical information. I have a couple minor change requests:

1. In the References section, remove the top 2 references to the DDS content since we moved the project to cdisc-org and you already have a link to that project (Data Definition Specification project), so we have the DDS covered.
2. In the References section, remove that final link to the DDS project charter as it is outdated and will be changing with the latest scope changes.
3. In the references section, remove the Define-XML generator (template2define) reference since this code has since been moved into our DDS project repo.
4. Under Current Status and Roadmap, remove Trial Design dataset generator and Spreadsheet-based loader (alternative to USDM) as these were recently de-prioritized (will get to them in a later phase).
5. Under Background, in the phrase "the DDE derives all the metadata needed to generate regulatory submission artifacts automatically," drop the word "automatically" because under How It Works, it mentions "any manually filled gaps into one validated model."

Thanks!