Adapt SMAC3 docs links

[LukasFehring]

Can we adapt the docs linked https://automl.github.io/SMAC3/main/ link to the current docs? I do not know how or where that would be possible.
This the highest-ranked link on Google, and might be confusing

[timruhkopf]

Fixed with commit #51f43c17

Here is how I did it:

1. go to the main branch,
2. mkdocs build --clean --> which creates a site/ directory.
3. Move this site directory to the gh-pages branch and replace the main directory with it (renaming it to "main" of course)
4. git add the folder, commit and push the gh-pages branch.

Clear the browser cache or use the incognito mode to see the changes.