add readme for MONAI + Fed-BioMed integration for federated learning (#1944)

Fixes # .

### Description
A few sentences describing the changes proposed in this pull request.

### Checks
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [x] Avoid including large-size files in the PR.
- ~~[ ] Clean up long text outputs from code cells in the notebook.~~
- ~~[ ] For security purposes, please check the contents and remove any
sensitive info such as user names and private key.~~
- [x] Ensure (1) hyperlinks and markdown anchors are working (2) use
relative paths for tutorial repo files (3) put figure and graphs in the
`./figure` folder
- ~~[ ] Notebook runs automatically `./runner.sh -t <path to .ipynb
file>`~~

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Signed-off-by: Marc Vesin <marc.vesin@inria.fr>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Eric Kerfoot <17726042+ericspod@users.noreply.github.com>