Fix AppVeyor status badge link in README.
Fix AppVeyor status badge link in README.

meshell/Cpp_project_template,meshell/Cpp_project_template,mariokonrad/Cpp_project_template,meshell/Cpp_project_template,mariokonrad/Cpp_project_template,mariokonrad/Cpp_project_template,meshell/Cpp_project_template