Fix docs and spec URLs in README

[chanix95]

Done

Changed invalid URLs with the ones that should be.

Invalid URLs in README:

• https://security.ubuntu.com/docs
• http://0.0.0.0:8030/spec
• http://0.0.0.0:8030/docs

Valid URLs:

• https://ubuntu.com/security/api/docs
• http://0.0.0.0:8030/security/api/spec.json
• http://0.0.0.0:8030/security/api/docs