fix run_clip README
# What does this PR do?

Fix `run_clip` example's README.

The path should be the absolute path to the downloaded data directory (using relative path will make `load_dataset` look for the data directory on the Hub).

From slack discussion:
- _basically the base path used to resolve relative path corresponds to where the dataset is loaded from_
- _relative paths are transformed to the corresponding URL in the repo the script comes from_

Fix #18291
_The documentation is not available anymore as the PR was closed or merged._