Adding a Computer Architecture Book. (#11121)

## What does this PR do?
Add resource(s)

## For resources
### Description
Adding a Computer Architecture Book.

### Why is this valuable (or not)?

### How do we know it's really free?
Licence: Creative Commons Attribution 4.0 License.


### For book lists, is it a book? For course lists, is it a course? etc.
It's a book.
## Checklist:
- [ :white_check_mark: ] Read our [contributing guidelines](https://github.com/EbookFoundation/free-programming-books/blob/main/docs/CONTRIBUTING.md).
- [ :white_check_mark: ] [Search](https://ebookfoundation.github.io/free-programming-books-search/) for duplicates.
- [ :white_check_mark: ] Include author(s) and platform where appropriate.
- [ :white_check_mark: ] Put lists in alphabetical order, correct spacing.
- [ :white_check_mark: ] Add needed indications (PDF, access notes, under construction).
- [ :white_check_mark: ] Used an informative name for this pull request.

## Follow-up

- Check the status of GitHub Actions and resolve any reported warnings!

books/free-programming-books-subjects.md

@@ -222,6 +222,7 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 
 * [Basic Computer Architecture](https://www.cse.iitd.ac.in/~srsarangi/archbooksoft.html) - Smruti R. Sarangi (HTML, PDF, Slides, Videos)
 * [Computer Organization and Design Fundamentals](https://faculty.etsu.edu/tarnoff/138292) - David Tarnoff (PDF)
+* [Digital Circuit Projects: An Overview of Digital Circuits Through Implementing Integrated Circuits - Second Edition](https://cupola.gettysburg.edu/cgi/viewcontent.cgi?article=1000&context=oer) - Charles W. Kann (PDF)
 
 
 ### Computer Science