docs: clean up systemPreferences.effectiveAppearance text

* Grammar fixes
* Add links for Electron Packager & Electron Forge
* Update Packager API links, given electron/packager#1131

docs/api/system-preferences.md

@@ -371,11 +371,11 @@ maps to [NSApplication.effectiveAppearance](https://developer.apple.com/document
 
 Please note that until Electron is built targeting the 10.14 SDK, your application's
 `effectiveAppearance` will default to 'light' and won't inherit the OS preference. In
-the interim in order for your application to inherit the OS preference you must set the
-`NSRequiresAquaSystemAppearance` key in your apps `Info.plist` to `false`.  If you are
-using `electron-packager` or `electron-forge` just set the `enableDarwinDarkMode`
-packager option to `true`.  See the [Electron Packager API](https://github.com/electron/electron-packager/blob/master/docs/api.md#darwindarkmodesupport)
-for more details.
+the interim, in order for your application to inherit the OS preference, you must set the
+`NSRequiresAquaSystemAppearance` key in your app's `Info.plist` to `false`.  If you are
+using [Electron Packager][electron-packager] or [Electron Forge][electron-forge], set the
+`darwinDarkModeSupport` packager option to `true`.  See the [Electron Packager
+API][packager-darwindarkmode-api] for more details.
 
 **[Deprecated](modernization/property-updates.md)**
 
@@ -481,8 +481,12 @@ maps to [NSApplication.effectiveAppearance](https://developer.apple.com/document
 
 Please note that until Electron is built targeting the 10.14 SDK, your application's
 `effectiveAppearance` will default to 'light' and won't inherit the OS preference. In
-the interim in order for your application to inherit the OS preference you must set the
-`NSRequiresAquaSystemAppearance` key in your apps `Info.plist` to `false`.  If you are
-using `electron-packager` or `electron-forge` just set the `enableDarwinDarkMode`
-packager option to `true`.  See the [Electron Packager API](https://github.com/electron/electron-packager/blob/master/docs/api.md#darwindarkmodesupport)
-for more details.
+the interim, in order for your application to inherit the OS preference, you must set the
+`NSRequiresAquaSystemAppearance` key in your app's `Info.plist` to `false`.  If you are
+using [Electron Packager][electron-packager] or [Electron Forge][electron-forge], set the
+`darwinDarkModeSupport` packager option to `true`.  See the [Electron Packager
+API][packager-darwindarkmode-api] for more details.
+
+[electron-forge]: https://www.electronforge.io/
+[electron-packager]: https://github.com/electron/electron-packager
+[packager-darwindarkmode-api]: https://electron.github.io/electron-packager/master/interfaces/electronpackager.options.html#darwindarkmodesupport