chore: Update github action example for newer versions

[sambarnes]

Related issue(s)

Resolves #32

Description

Summary of changes

fixes the readme & bumps version so newcomers more likely to pin latest

Dependency additions / changes

N/A

Test additions / changes

N/A

Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt with default settings.
• I have linked this PR to the issue(s) that it resolves.
• I have reviewed the changes on GitHub, line by line.
• I have ensured all changes are covered in the description.

[sambarnes]

was originally trying to slip into @TomAFrench 's branch here: #30

but feel free to change the base to whatever you want

[TomAFrench]

Thank you for updating version to toolchain, we must have missed that.

I've changed the base to main as the original branch is an automated release branch which we shouldn't build on top of (it just handles making a release with the contents of main).