Add more comments

[AArnott]

Add readme.md files to each folder, describe contents, why folks want it or may want to delete it.

[AArnott]

Also add a doc folder with a readme as a "put your docs here" folder.

[AArnott]

Link to the .NET OSS Library guidance page and call out that it conforms to it.

[AArnott]

Call out principles that this template holds to.