Docs for Official Repo release

Changes and additions for the Official Repo release on Wednesday.
I wonder, given the previous advice of using `WORKDIR`, `ENV` and others, if this should not be written differently

however, I on reflection I would probably write


```
    RUN mdkir -p /usr/src/things && \
        cd /usr/src/things && \
        curl -SL http://example.com/big.tar.gz | tar -xJC . && \
        make all
```