Add npm token to documentation

Signed-off-by: BOUHOURS Antoine <antoine.bouhours@rte-france.com>

README.md

@@ -28,6 +28,7 @@ you need to follow the steps below:
 - [Make a release action](https://github.com/powsybl/powsybl-diagram-viewer/actions/workflows/release.yml)
 - In the 'run workflow' combobox select, let the branch on main
 - Enter the type of evolution (major | minor | patch)
+- Enter your NPM access token (see [access token documentation](https://docs.npmjs.com/creating-and-viewing-access-tokens) for details)
 - Click 'run workflow'
 
 Notes :