[BUG] - docker tags are wrong in the README.md and run.py

[bids-apps]

[BUG] - docker tags are wrong in the README.md and run.py

[Remi-Gau]

silly question, do we want those tags to work?

docker pull bids/freesurfer:6
docker pull bids/freesurfer:7

meaning that currently: 7-202309 == 7.4.1-202309

but we may want: 7 == 7-latest == 7-202309 == 7.4.1-202309

[SamGuay]

From a user perspective, I (naively) assumed that copy/paste would work, then I had to go and find the specific tag on docker hub. IMO, having a working tag (7-latest) would be a good start then link to docker hub since it is not that obvious which account is the official one to get all the tags.

Note that once default/latest is changed to v7, it should be less of a problem.

[Remi-Gau]

OK so one PR to update the README for now and we can see for the next release if we want to have more tags.