GitHub: Linking to an issue from a wiki page

It doesn't happen in wiki documents.

You can use a relative url but it isn't that much of a shortcut. It also depends on where you are in the project.

For example in the Readme.md in the master branch of the project:

[#1](../../issues/1)

On the github wikis:

[#1](../issues/1)

Anywhere:

[#1](/user/project/issues/1)
(h/t to VertigoRay for suggesting this)