Ignore QtCreator project settings

QtCreator stores a file containing amongst other things the path to where
your build tree is and what parameters you used for the configuration
process. These data is user-specific and should not be stored in version
control.

If you open the project in QtCreator again after having made changes
to CMakeLists.txt outside of it, it may create a new user file which
should be ignored just like the original.

.gitignore

@@ -17,6 +17,9 @@
 .project
 .settings/*
 
+# QtCreator project settings
+CMakeLists.txt.user*
+
 # in-tree build with CMake
 CMakeCache.txt
 CMakeFiles/