Ignore CLion build directory.

.gitignore

diff --git a/.gitignore b/.gitignore
index 9807462..44bb56b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,3 +7,4 @@
 *.tar.xz
 /.clangd
 /compile_commands.json
+/cmake-build-debug