step-by-step for adding license notes

[eshellman]

#11260 proposed adding licence notations.
#11269 gave an example, passing the linter tests.

We are now requesting PRs to add this info to our repo!

In preparation for beginning to accept PR's which add licenses, This issue proposes a step-by-step workflow to make clear how these are to be added.

1. Select an item, preferably a book. (I found a bunch by searching merged PRs for "Creative Commons")
2. Access the book, and look for a license statement. For example, in the book added in Update free-programming-books-langs.md with "Computational and Inferential Thinking" #9010 the contributor found the text:

"The contents of this book are licensed for free consumption under the following license: 

 [Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)](https://creativecommons.org/licenses/by-nc-nd/4.0/)."

3. We're ignoring license variants, so the text to be added to our listing should be (CC BY-NC-ND) (note the leading space) At this time we are NOT accepting notations for licenses other than Creative Commons (CC) and the Gnu Free Documentation License (GFDL).
4. For each item you're adding a license to, write a sentence in your PR about where you found the license statement.
5. Don't add license notes for more than one section at at time, and it's ok to do one item for a PR. If you add more than 5 license additions at a time, it will discourage PR reviewers from checking the PR.

Comments, questions and test PRs welcome!

[manvith12]

hey! , i was working on this.
i found a few books where no copyright was mentioned any idea what to do about them?
for example : a beginners guide to matlab