Add remark about git submodules to readme and add git logo for some color

Author: tschuchortdev

Diff for: README.md

@@ -1,9 +1,12 @@
+<img src="https://git-scm.com/images/logos/downloads/Git-Icon-1788C.png" align="right"
+     title="Git Logo" width="120">
+
 # CMake Git Clone
 ![build status](https://travis-ci.org/tschuchortdev/cmake_git_clone.svg?branch=master) [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT) [![contributions welcome](https://img.shields.io/badge/contributions-welcome-brightgreen.svg?style=flat)](https://github.com/tschuchortdev/cmake_git_clone/issues)
 
 CMake module to automatically clone git repositories during configure time.
 
-This can be useful if you have CMake-only libraries such as [ucm](https://github.com/onqtam/ucm) that have no build script but have to be available at configure time. `ExternalProject_Add` can not be easily used for this because it executes at build time and only if other targets depend on it.
+This can be useful if you have CMake-only libraries such as [ucm](https://github.com/onqtam/ucm) that have no build script but have to be available at configure time. `ExternalProject_Add` can not be easily used for this because it executes at build time and only if other targets depend on it. In contrast to other solutions `cmake_git_clone` also handles nested git submodules correctly automatically.
 
 ## Usage: