tweaks

tests #11260

books/free-programming-books-subjects.md

@@ -786,8 +786,8 @@ Kerridge (PDF) (email address *requested*, not required)
 * [Principled Programming / Introduction to Coding in Any Imperative Language](https://www.cs.cornell.edu/info/people/tt/Principled_Programming.html) - Tim Teitelbaum
 * [Programming and Programming Languages](https://papl.cs.brown.edu/2019/) - Shriram Krishnamurthi
 * [Programming Languages: Application and Interpretation (2nd Edition)](https://cs.brown.edu/~sk/Publications/Books/ProgLangs/) - Shriram Krishnamurthi
-* [Structure and Interpretation of Computer Programs](https://web.mit.edu/6.001/6.037/sicp.pdf) - Harold Abelson, Gerald Jay Sussman, Julie Sussman (PDF)
-* [Structure and Interpretation of Computer Programs](https://sarabander.github.io/sicp/html/index.xhtml) - Harold Abelson, Gerald Jay Sussman, Julie Sussman (HTML)
+* [Structure and Interpretation of Computer Programs](https://web.mit.edu/6.001/6.037/sicp.pdf) - Harold Abelson, Gerald Jay Sussman, Julie Sussman (PDF) (CC BY-SA)
+* [Structure and Interpretation of Computer Programs](https://sarabander.github.io/sicp/html/index.xhtml) - Harold Abelson, Gerald Jay Sussman, Julie Sussman (HTML) (CC BY-SA)
 * [The Black Art of Programming](http://self.gutenberg.org/wplbn0002828847-the-black-art-of-programming-by-mcilroy-mark.aspx?) - Mark McIlroy
 * [The Craft of Programming](https://kilthub.cmu.edu/articles/The_Craft_of_Programming/6610514) - John C. Reynolds
 * [The Nature of Code](https://natureofcode.com/book) - Daniel Shiffman (HTML)

docs/CONTRIBUTING.md

@@ -140,6 +140,23 @@ Example:
     ```text
     GOOD: * [A Way-backed Interesting Book](https://web.archive.org/web/20211016123456/http://example.com/) - John Doe (HTML) *(:card_file_box: archived)*
     ```
+    
+- <a id="license"></a>Free Licenses (While we include resources that are "All Rights Reserved" but free to read, we encourage the use of free licenses, such as Creative Commons):
+
+    ```text
+    GOOD: * [A Very Awesome Book](https://example.org/book.pdf) - Jane Roe (PDF) (CC BY-SA)
+    ```
+
+    Supported Licences (no versioning):
+
+    - `CC BY` 'Creative Commons attribution'
+    - `CC BY-NC` 'Creative Commons non-commercial'
+    - `CC BY-SA` 'Creative Commons share-alike'
+    - `CC BY-NC-SA` 'Creative Commons non-commercial, share-alike'
+    - `CC BY-ND` 'Creative Commons no-derivatives'
+    - `CC BY-NC-ND` 'Creative Commons non-commercial, no-derivatives'
+    - `GFDL` 'Gnu Free Documentation License'
+
 
 ### Alphabetical order