Removed README-git.md

We're fully hosted on GitHub, no need for additional explanation.

docs/README-git.md

@@ -1,16 +0,0 @@
-git
-=========
-
-The latest development version of SDL is available via git.
-Git allows you to get up-to-the-minute fixes and enhancements;
-as a developer works on a source tree, you can use "git" to mirror that
-source tree instead of waiting for an official release. Please look
-at the Git website ( https://git-scm.com/ ) for more
-information on using git, where you can also download software for
-macOS, Windows, and Unix systems.
-
-    git clone https://github.com/libsdl-org/SDL
-
-There is a web interface to the Git repository at:
-	http://github.com/libsdl-org/SDL/
-