Missing guidance on how to include an image in a blog post

[jieyouxu]

E.g. in #1425 I can't seem to find a path that would show up properly in local static site build (via cargo build or cargo serve -p) but then it matches what other Inside Rust blog post uses...

[jieyouxu]

(FWIW, the inside-rust blogs need another layer of ../ versus if the blog was for the public-facing blog)

[jieyouxu]

For my future self, mostly: note that Inside Rust image folder has an extra inside-rust/ folder. The inline relative path from the Inside Rust blog post should look something like

![Sample job summary](../../../../images/inside-rust/test-infra-jan-feb-2025/example-ci-job-summary.png)