also keep summary MACAW results in a text file

[edkerk]

Current behavior:

MACAW tests are run as part of each PR, while summary results are posted as a comment (example), and more detailed results are committed in the macawResults folder. In the cited example (from PR #829), it is not that obvious that 482 more reactions were found in the category "reversible reactions that can only carry steady-state fluxes in a single direction due to dead-ends." when compared to the previous PR #840.

Expected feature/value/output:

For easier comparison of MACAW results with previous results, it would be useful to have the summary results also written in macawResults/README.md, so that the diff of the new commit clearly highlights the changes.