Adds badge of appveyor build system

Author: micwypych

README.md

@@ -1,6 +1,12 @@
 ### C++ programming classes problmes ###
 
 [![Build Status](https://travis-ci.org/micwypych/cpp-exercises.svg?branch=master)](https://travis-ci.org/micwypych/cpp-exercises)
+[![Build status](https://ci.appveyor.com/api/projects/status/39thleljhjmtof0t?svg=true)](https://ci.appveyor.com/project/micwypych/cpp-exercises)
+
+After cloning please replace badges with your project's badges
+
+For [travis](https://travis-ci.org) replace in the README.md micwypych with your nickname from github and cpp-exercises with your project name on github
+For [appveyor](https://ci.appveyor.com), go to the settings -> badges -> sample markdown code and replace second badge code
 
 #### CLion CMakeLists.txt template ####