Proposed changes

Update external URLs which were being automatically redirected to ensure that the links don't break when such redirection is removed by the external website.

The redirected URLs were found by using becheran/mlc

cargo install mlc
mlc --gitignore --root-dir . --throttle 100

Whilst this is not critical work it ensures that our documentation stays up to date.

Notes:

• https://www.identrust.com/dst-root-ca-x3 is still being redirected, but I haven't been able to find a suitable replacement yet
• Raspberry Pi website links (https://www.raspberrypi.com) register as false positives in mlc as it seems their website prevents crawlers/spiders and the mlc client returns a HTTP 403 when trying to verify the links, but the links can be manually verified in the browser

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• Documentation Update (if none of the other choices apply)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Paste Link to the issue

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA (in all commits with git commit -s)
• I ran cargo fmt as mentioned in CODING_GUIDELINES
• I used cargo clippy as mentioned in CODING_GUIDELINES
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments