Update and/or fix IBM Cloud docs links

[eiri]

Checklist

• [x] Tick to sign-off your agreement to the Developer Certificate of Origin (DCO) 1.1
• [ ] Added tests for code changes or test/build only changes
• [ ] Updated the change log file (CHANGES.md|CHANGELOG.md) or test/build only changes
• [x] Completed the PR template below:

Description

Update links to IBM Cloud™ documentation site to new paths in README. Link to api#ping removed as it is not on API docs anymore.