Wikis are just Git repositories, you can make changes locally and push them to your repository. But you have to clone it separately.
Add .wiki.gitto repository name.
That is, if your repository name was foobar:
git clone git@github.com:myusername/foobar.git
is the way to clone your repository and
git clone git@github.com:myusername/foobar.wiki.git
is the way to clone your wiki.
wiki :

clone https, ssh clone, , .
ssh:
git@<host>:<username>/<repo_name>.wiki.git
, , . -, , , .