docs: update mojave-dark-mode-guide.md

[JB1905]

Add info about dark mode support in electron-builder

Description of Change

Add info about dark mode support in electron-builder in mojave-dark-mode-guide.md

Release Notes
Notes: Add info about dark mode support in electron-builder in mojave-dark-mode-guide.md

[welcome]

💖 Thanks for opening this pull request! 💖

We use semantic commit messages to streamline the release process. Before your pull request can be merged, you should update your pull request title to start with a semantic prefix.

Examples of commit messages with semantic prefixes:

• fix: don't overwrite prevent_default if default wasn't prevented
• feat: add app.isPackaged() method
• docs: app.isDefaultProtocolClient is now available on Linux

Things that will help get your PR across the finish line:

• Follow the JavaScript, C++, and Python coding style.
• Run npm run lint locally to catch formatting errors earlier.
• Document any user-facing changes you've made following the documentation styleguide.
• Include tests when adding/changing behavior.
• Include screenshots and animated GIFs whenever possible.

We get a lot of pull requests on this repo, so please be patient and we will get back to you as soon as we can.

[codebytere]

@JB1905 it looks like you deleted the issue template, please go back and fill that out. Missing fields will fail CI checks like the release-notescheck.

[ckerr]

(FYI cc @MarshallOfSound)

[MarshallOfSound]

I think the builder reference should be put in a new paragraph beneath this one with its own links to builders option name. Builders option is not the same as forges / packagers.

[release-clerk]

Release Notes Persisted

Add info about dark mode support in electron-builder in mojave-dark-mode-guide.md

[welcome]

Congrats on merging your first pull request! 🎉🎉🎉