Add ccls cache to gitignore (#31437)

Summary:
`ccls` [puts a cache](https://github.com/MaskRay/ccls/wiki/Customization#cachedirectory) in the working directory by default, this PR adds it to gitignore so git doesn't pick it up
](https://our.intern.facebook.com/intern/diff/19165007/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31437

Pulled By: driazati

Differential Revision: D19165007

fbshipit-source-id: 41012eb0ece2df60b8566d7929710b154c38ee66
diff --git a/.gitignore b/.gitignore
index 4892fe0..e01a1b1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -250,3 +250,7 @@
 GPATH
 tags
 TAGS
+
+
+# ccls file
+.ccls-cache/