Improve documentation in the README files

[adityapatwardhan]

The README files need to be updated to explain the new workflow.

[andyleejordan]

Since history was not retained in the export (git subtree would have accomplished this 😉), I think that we probably want to add a reference to where this code lived originally so that future maintainers can easily trace back development history. (This could probably be as simple as the git log ... commands of the paths back in the PowerShell repo to look at the history of the deleted files.)

Awesome news removing the last submodule, that's fantastic.