feat(_include/footer.html): add google anayltics info
feat(_include/footer.html): add google anayltics info

leanprover/leanprover.github.io,avigad/leanprover.github.io,soonhokong/leanprover.github.io,avigad/leanprover.github.io,fpvandoorn/leanprover.github.io,avigad/leanprover.github.io,soonhokong/leanprover.github.io,soonhokong/leanprover.github.io,leanprover/leanprover.github.io,fpvandoorn/leanprover.github.io,leanprover/leanprover.github.io,fpvandoorn/leanprover.github.io