deploy formule to gh pages

[miguelgrc]

Closes #26

• The demo is now deployed at https://cern-sis.github.io/react-formule/ and redeploys automatically on push/merge to master.
• It shows the deployed version number in the footer (which is simply the version in package.json, since we're not deploying npm releases but the current master branch) for more clarity.
• This can be revisited if we ever change our git workflow (e.g. if we decide to work on a dev branch and manually merge dev to master each time we want to release a new version and have the publish action auto-publish to npm from master).

[github-actions[bot]]

:tada: This PR is included in version 1.0.0 :tada:

The release is available on:

• npm package (@semantic-release-github-plugin dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: