An update on book6

[Brian E Carpenter]

Hi,

Please have a look at the progress so far on "the book":

https://github.com/becarpenter/book6/blob/main/Contents.md

Issues and discussion should be raised on GitHub, rather than here.

Most of the text remains to be written, and the book itself tells you how to do that. Please contribute!
   
Regards
     Brian Carpenter