Rework RELEASE.md to account for release candidates and branching strategy

Our current [RELEASE.MD](https://github.com/fairpm/fair-plugin/blob/main/RELEASE.MD) outlines the release process if we're working again a single branch, `main`. With the introduction of our [branching strategy](https://github.com/fairpm/tsc/blob/main/process/release-branching.md), the release instructions should be updated to account for release candidates.