chore: add inst/ to gitignore

[Pranavchiku]

Fixes the problem of

% git status
On branch main
Your branch is up to date with 'origin/main'.

Untracked files:
  (use "git add <file>..." to include in what will be committed)
	inst/

nothing added to commit but untracked files present (use "git add" to track)

[Shaikh-Ubaid]

It looks good to me. Thanks.