You can edit the authorized_extensions admin setting to allow upload of .zips:
On this site, the admin has enabled uploading of .pdf files and files with no extension by adding |.pdf| on the end.
However, I suggest using Gist if you need to quickly share multiple code files without assets like images.
All of the GitHub /user/repo/blob/... URLs onebox nicely in Discourse, so you can use that too.