Create a markdown document with existing CVRF repositories about csaf

[santosomar]

RedHat's CVRF from Langley: https://access.redhat.com/documentation/en-us/red_hat_security_data_api/1.0/html-single/red_hat_security_data_api/index#cvrf

[santosomar]

Cisco CVRF repo: https://tools.cisco.com/security/center/cvrfListing.x

[santosomar]

During the CSAF 2.0 working session today, we discussed the potential of documenting a list of existing CVRF repositories in the industry (along with a good few examples for Eric to further test the parsing and translation of CVRF/CSAF documents).

I started a list of known CVRF repositories from different vendors, MITRE, and the community in our GitHub repository at:

https://github.com/oasis-tcs/csaf/blob/master/sandbox/CVRF_repositories.md

I am very sure that I missed several. Please feel free to add more via a pull request.

This email and notification was also sent to the OASIS CSAF TC:
https://lists.oasis-open.org/archives/csaf/201905/msg00003.html