Fill out VSCode changelog add release instructions

[dotNomad]

This PR fills out a bit of the VSCode Extension CHANGELOG.md that is bundled with the extension, and adds instructions to the CONTRIBUTING.md guide to update it.

When we do the next release we can change the Unreleased header to 1.1.9

Intent

Resolves #1783

Type of Change

• • [ ] Bug Fix
• • [ ] New Feature
• • [ ] Breaking Change
• • [x] Documentation
• • [ ] Refactor
• • [ ] Tooling