* docs: clean up systemPreferences.effectiveAppearance text
* Grammar fixes
* Add links for Electron Packager & Electron Forge
* Update Packager API links, given https://github.com/electron/electron-packager/pull/1131
* docs: clean up Dark Mode guide
* Grammar fixes
* Add links for Electron Packager & Electron Forge
* docs: adjust based on Electron 8 using 10.14 SDK