Shut down this repo

[ramonawalls]

With the MIxS 6 release, we will no longer need this repo. I suggest that we maintain MIxS as linkml in its separate repo (https://github.com/GenomicsStandardsConsortium/mixs) and then push the code for web pages over to the website repo (https://github.com/GenomicsStandardsConsortium/gensc.github.io).

[ramonawalls]

All open issues have been moved to the main MIxS repo.