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)
@@ -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