I very much support the sentiment - I also would love to see a bioinformatics handbook using Julia - but I’m afraid you can’t just fork the content of the BioStar Handbook and replace the code examples with Julia.
The BioStar Handbook is not free, see FAQ – The Biostar Handbook for the rationale.
And in the book itself, you find the following clauses:
"2.0.3 What are the licensing terms?
The Handbook’s content is copyrighted material owned by Biostar Genomics LLC . Republishing any part of the Handbook is permitted only on a limited basis and must follow the terms of the Fair Use policy unless other, prior agreements have been made.
2.0.4 What can I reuse from the book?
If you own the book or have an account on this site that means that you have been provided with a license to access, apply, modify and reuse information from the book as it pertains to your own work and research."