Update filename-macros.md

[colin-home]

Change escaping for asterisks to something that should render properly.

[PRMerger18]

Microsoft authors of articles need to make updates through the private repository so the updates can be staged and validated by the current validation rules. After you review staging and fix all validation issues, you can add the sign-off comment to let the PR reviewers know the updates are ready to be merged.It's easy to access the private repo version of your articles in GitHub. Just add -pr to the URL, as follows:
Public repo URL: https://github.com/Microsoft/azure-docs/blob/master/articles/azure-portal-overview.md
Private repo URL: https://github.com/Microsoft/azure-docs-pr/blob/master/articles/azure-portal-overview.md
We have closed this pull request. Please resubmit the updates through the private repo. If you need perms to the private repo, see the contributor guide instructions