docs: fix dead links in README

[dalelane]

Noticed a couple of dead links in the README doc. One is a typo (AUTHENTICATION.md should be Authentication.md) so I fixed that.

The other pointed at a doc on VCAP_SERVICES that doesn't exist any more, so I changed it for the only description I could find for VCAP_SERVICES on the public cloud docs site.

Signed-off-by: Dale Lane [email protected]

[CLAassistant]

All committers have signed the CLA.

[apaparazzi0329]

The VCAP_SERVICES link is out of date again but it is a fairly outdated form of authentication that we will have to revisit in terms of our documentation