Update guidance on recording dependencies

[foster999]

We should give a clearer steer on pinning dependency versions:

• Packages of reusable code should use more than or equal to (e.g. pandas>=1.0.0) version for each dependency. This gives users of the package flexibility in their pipeline requirements. Use not equal to if you find that a specific version doesn't work with your package (e.g. pandas>=1.0.0.,!=1.2.0)
• Applications or pipelines should specify exact versions for all dependencies, for reproducibility (e.g. pandas==1.5.3)