Update README.md and project description

Now that we have shifted the project template to Drupal.org, we need to complete a few housekeeping tasks:

1. Update the README.md with the new namespaces.
2. Update the project description page to mirror the new README.
3. Require drupal/sector instead of sparksinteractive/sector-distribution (when the infra team completes the project type change)
4. Create a stable release tag (when Sector had a stable 10 release)
5. Lock and deprecate the old Github repository, linking it here.
6. Update the "install" instructions to include the flag to ignore git history and accept all prompts by default.