Add RSS autodiscovery to blog

[tynandebold]

Description

Resolves #159

Development notes

Added the necessary link tag to the blog homepage and article pages.

QA notes

Check the HTML source of the blog homepage and article pages.

Checklist

• [ ] Opened this PR as a 'Draft Pull Request' if it is work-in-progress
• [ ] Added tests to cover my changes, where applicable

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