add source code links/licenses/languages for version control systems

README.md

@@ -654,9 +654,9 @@ Troubleshooting tools.
 
 Software versioning and revision control.
 
-- [Darcs](http://darcs.net/) - Patch-based distributed version control (more info: [wiki](http://darcs.net/Theory/PekkaPatchTheory))
-- [Fossil](http://www.fossil-scm.org/) - Distributed version control with built-in wiki and bug tracking.
-- [Git](http://git-scm.com/) - Distributed revision control and source code management (SCM) with an emphasis on speed.
+- [Darcs](http://darcs.net/) - Cross-platform version control system, like git, mercurial or svn but with a very different approach: focus on changes rather than snapshots. ([Source Code](https://darcs.net/releases/)) `GPL-2.0` `Haskell`
+- [Fossil](http://www.fossil-scm.org/) - Distributed version control with built-in wiki and bug tracking. ([Source Code](https://www.fossil-scm.org/home/dir?ci=trunk)) `BSD-2-Clause` `C`
+- [Git](http://git-scm.com/) - Distributed revision control and source code management (SCM) with an emphasis on speed. ([Source Code](https://github.com/git/git)) `GPL-2.0` `C`
 - [GNU Bazaar](http://bazaar.canonical.com/) - Distributed revision control system sponsored by Canonical.
 - [Mercurial](https://www.mercurial-scm.org/) - Another distributed revision control.
 - [Subversion](http://subversion.apache.org/) - Client-server revision control system.