Create walkthrough blog post

[zacharybmeyers]

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Description

Moves the content from the walkthrough in #4361 to a new blog post.

To Do

• [ ] Documentation. (If you've add a new command-line flag, for example, find the appropriate page under docs/ to describe it.)
• [x] Changelog. (Add an entry to docs/changelog.rst near the top of the document.)
• [ ] Tests. (Encouraged but not strictly required.)

[zacharybmeyers]

Apologies it took me a little bit to look back into this, thank you for those grammar suggestions. I'm happy with how this is looking and glad it will get published! Let me know if there are any further changes you'd like to see.

[sampsyo]

Here's the public URL for the blog post, FYI! https://beets.io/blog/walkthrough.html