Ignore Qt Creator project files (#1702)

diff --git a/.gitignore b/.gitignore
index 98fbb21..61e1c62 100644
--- a/.gitignore
+++ b/.gitignore
@@ -36,3 +36,6 @@
 # Visual Studio Code project files
 /.vscode/
 /.ccls-cache/
+
+# Qt Creator project files
+/CMakeLists.txt.user