Add references to other CVE Services clients to README

[Vijay Sarvepalli]

This is more of an FYI, so you will be aware of related work. We CERT/CC attempting a smaller Javascript version of this client mostly inspired by this project, as well as Vulnogram and https://github.com/xdrr/cve.js work. The aim is to simplify an interface for usage by small/mid-size CNA's.

https://github.com/CERTCC/cveClient

Thanks
Vijay