Use HTML relative paths for tiles in the docs
_The documentation is not available anymore as the PR was closed or merged._ > Good catch, @lewtun. Thanks for the fix.
> 
> Do you know if there are other absolute paths in the docs that should be fixed as well?

I found a few more in [0d4796b](https://github.com/huggingface/datasets/pull/5092/commits/0d4796b747e6620d9fcc17a8f74acc5cf4bba7be).

However, I noticed that none of the cross-references (e.g. to API classes / methods) work locally, but that is probably just a limitation of the local build Thanks.
This PR replaces the absolute paths in the landing page tiles with relative ones so that one can test navigation both locally in and in future PRs (see [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_5084/en/index) for an example PR where the links don't work).

I encountered this while working on the `optimum` docs and figured I'd fix it elsewhere too :)

Internal Slack thread: https://huggingface.slack.com/archives/C02GLJ5S0E9/p1665129710176619