feat: add vcs section

handles proposal(lists): Merge Version Control Systems into same section EbookFoundation#5526

books/free-programming-books-subjects.md

@@ -44,6 +44,7 @@ Books that cover a specific programming language can be found in the  [BY PROGRA
 * [Software Architecture](#software-architecture)
 * [Standards](#standards)
 * [Theoretical Computer Science](#theoretical-computer-science)
+* [Version Control Systems](#version-control-systems)
 * [Web Performance](#web-performance)
 * [Web Services](#web-services)
 * [Workflow](#workflow)
@@ -724,7 +725,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [Intrusion Detection Systems with Snort](http://ptgmedia.pearsoncmg.com/images/0131407333/downloads/0131407333.pdf) (PDF)
 * [OpenSSL Cookbook](https://www.feistyduck.com/library/openssl-cookbook/)
 * [OWASP Mobile Security Testing Guide](https://mobile-security.gitbook.io/mobile-security-testing-guide/) - Bernhard Mueller et al.
-* [OWASP Testing Guide 4.0](https://www.owasp.org/images/1/19/OTGv4.pdf) (PDF)
+* [OWASP Testing Guide 4.2](https://owasp.org/www-project-web-security-testing-guide/v42/) - The OWASP® Foundation (HTML, [PDF](https://github.com/OWASP/wstg/releases/download/v4.2/wstg-v4.2.pdf))
 * [OWASP Top 10 for .NET Developers](http://www.troyhunt.com/2011/12/free-ebook-owasp-top-10-for-net.html)
 * [Security Engineering](http://www.cl.cam.ac.uk/~rja14/book.html)
 * [The Joy of Cryptography (2021)](https://web.engr.oregonstate.edu/~rosulekm/crypto/) - Mike Rosulek (PDF) (:construction: *in process*)
@@ -806,6 +807,11 @@ Kerridge (PDF) (email address *requested*, not required)
 * [Think Complexity](https://greenteapress.com/wp/think-complexity-2e/) - - Allen B. Downey (2nd Edition) (PDF, HTML)
 
 
+### <a id="version-control-systems"></a><a id="git"></a><a id="svn"></a><a id="mercurial"></a>Version Control Systems
+
+<!-- Waiting to add in -->
+
+
 ### Web Performance
 
 * [Book of Speed](http://www.bookofspeed.com) - Stoyan Stefanov