docs: Add new book title in technical communication list

docs/books.rst

@@ -17,6 +17,7 @@ Technical communication
 * `The Product is Docs <https://www.splunk.com/en_us/blog/splunklife/the-product-is-docs.html>`_, by Christopher Gales - **1st edition read in our book club**
 * `Wicked, Incomplete, and Uncertain: User Support in the Wild and the Role of Technical Communication <https://www.goodreads.com/book/show/37864792-wicked-incomplete-and-uncertain>`_, by Jason Swarts
 * `Software Technical Writing: A Guidebook <https://jamesg.blog/book.pdf>`_, by James Gallagher
+* `The Docs as Code Primer: A practical handbook <https://leanpub.com/thedocsascodeprimer>`_, by Gijs Reijn
 
 E-Learning
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