Adhere to new Eclipse Foundation repo content rules

Some new rules have come to light:

• Colleagues working on the Eclipse TRACE4CPS project were informed that the website repo also needs to contain the mandatory files. See eclipsefdn/emo-team/emo#658 (comment 1656259). We don't have such file yet, so we should add them. I propose to indicate that it is a deployment website, and that issues, merge requests, etc go to the main repo.
• According to the December 2023 Eclipse Office Hours, slide 9, we need some changes in the mandatory files in the main ESCET repo as well (check the video). We do have this info, but not directly in these files:
  • Describe how to locally build your project, either in the README or in the CONTRIBUTING file.
  • Describe also where development occurs (branch names, main branch).