There does not seem to be a way to track the wiki directory inside the project directory. But you can link to files in the project repository from the wiki. Example:
[README from default](https://bitbucket.org/owner/repository/src/tip/README.md)
[README from feat-aa](https://bitbucket.org/owner/repository/src/aa/README.md)
[Some other file](https://bitbucket.org/owner/repository/src/tip/doc/SOMEFILE.md)
You can even embed pictures hosted in the repository by putting "raw" in the url when using the ![]()
syntax:
![A image](https://bitbucket.org/owner/repository/raw/tip/image.png)
If you use the Creole syntax instead of markdown, there is even an easier way.