Add .clangd-index to .git-ignore

The clangd language server creates .clangd-index/ for it's index. This
should be ignored by git.

Bug: none
Change-Id: I333be7033d182468c409d7a2598e6752296beeb5
Reviewed-on: https://chromium-review.googlesource.com/c/1479650
Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: kylechar <kylechar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#633919}
1 file changed