[Epic] Add learning course for the book

[binkley]

We'd like to provide a learning repo/course for the book.
An example is the GitHub course-repo on CodeQL: https://github.com/skills/introduction-to-codeql.

Tech analysis

$ find . -type f | grep -v '/\.git/'
There is a .github/steps directory interrelated to the expected .github/workflows directory.
There are also "magic" sections of README.md, such as the top:

<!--
  <<< Author notes: Course header >>>
  Read <https://skills.github.com/quickstart> for more information about how to build courses using this template.
  Include a 1280×640 image, course name in sentence case, and a concise description in emphasis.
  In your repository settings: enable template repository, add your 1280×640 social image, auto delete head branches.
  Next to "About", add description & tags; disable releases, packages, & environments.
  Add your open source license, GitHub uses the MIT license.
-->

# Enable CodeQL to secure your source code

_Ensuring the security of application source code is a critical step in modern software development. In this GitHub Skills course, you will learn to use GitHub code scanning to identify, resolve, and prevent insecure coding patterns._

</header>

<!--
  <<< Author notes: Step 2 >>>
  Start this step by acknowledging the previous step.
  Define terms and link to docs.github.com.
  TBD-step-2-notes.
-->

Refs

• https://github.com/skills/introduction-to-codeql as an example