In addition to Roberts answer I would like to expand this a little.
On the very bottom of every site it is stated
user contributions licensed under cc by-sa 3.0 with attribution required
If you follow the attribution required you will get to a list, what you should be doing:
- Visually indicate that the content is from Stack Overflow or the Stack Exchange network in some way. It doesn’t have to be obnoxious; a discreet text blurb is fine.
- Hyperlink directly to the original question on the source site (e.g., http://stackoverflow.com/questions/12345)
- Show the author names for every question and answer
- Hyperlink each author name directly back to their user profile page on the source site (e.g., http://stackoverflow.com/users/12345/username)
Now for wiki entries, numbers 3 & 4 is honestly a little bit complicated, as usually it is not at all obvious (you will have to dive into the history).
I therefore think it should be sufficient if you just include the full URL to the tag-wiki entry.