Hlrs readm es

See merge request committees/hpc!14

- The main README.md file (landing page) provides
  now an overview of the benchmark suite
- Description of an individual case is provided in
  the README.md located in the root directory of
  the case. This description is linked within the
  landing page.
- For an intuitive navigation every case from the
  landing page is supplied with a thumbnail image

Added industrial benchmark cases I7 and I9 + minor changes

See merge request committees/hpc!8

Merge new and updated exaFOAM cases into HPC repo

See merge request committees/hpc!7