new instructions for windows users (quasarframework#5973)

The instructions for windows users were not correct given the state of things in December 2019. In addition to the software listed on this page to install, I had to install the JDK separately and gradle separately. And Cordova has moved on and now requires android-28 SDK to be installed or it wont work. 

I have followed the new instructions in this PR and tested that it worked properly. I pass the cordova requirements check.

Author: gregveres

docs/src/pages/quasar-cli/developing-cordova-apps/preparation.md

@@ -30,18 +30,30 @@ PATH=$PATH:$ANDROID_HOME/tools; PATH=$PATH:$ANDROID_HOME/platform-tools
 
 #### Windows
 
+After installing Android Studio, you need to install two more pieces of software:
+* JDK from Oracle. It can be found [here](https://www.oracle.com/java/technologies/jdk8-downloads.html)
+* Gradle. It used to usable from Android Studio but now you have to install it separately. There is a very specific version that cordova requires. You can download it [here](https://downloads.gradle-dn.com/distributions/gradle-4.10.3-all.zip)
+
+Then you will have to set environment variables. You will need to set the following variables. Cordova has a good guide for it already. It can be found [here](https://cordova.apache.org/docs/en/latest/guide/platforms/android/#setting-environment-variables). You need to:
+* add ANDRIOD_HOME. It can safely be set to: "%USERPROFILE%\AppData\Local\Android\Sdk"
+* add two ANDROID_HOME directories to your path: %ANDROID_HOME%\tools;%ANDROID_HOME%\platform-tools
+* add Gradle to your path. Note that gradle does not have an installer. You just put the binary files where you want them, then add the bin directory to your path.
+
+If you have an init script for your command prompt or powershell, you can try this:
 ```bash
 setx ANDROID_HOME "%USERPROFILE%\AppData\Local\Android\Sdk"
-setx path "%path%;%ANDROID_HOME%\tools;%ANDROID_HOME%\platform-tools"
+setx path "%path%;%ANDROID_HOME%\tools;%ANDROID_HOME%\platform-tools;<gradle_path>\bin;"
 ```
 
+After the tools are installed, setup Android Studio with the correct SDK and create a virtual machine. 
+
 * Start Android studio by changing into the folder you installed it in and run `./studio.sh`. Next step is to install the individual SDKs:
 
 * Open the "Configure" menu at the bottom of the window:
 
   ![SDK manager](https://cdn.quasar.dev/img/Android-Studio-SDK-Menu.png "SDK manager")
 
-* Select the desired SDKs. As per August 2018 Cordova supports 5.0 and up and click on "Apply" to install the SDKs.
+* Select the desired SDKs. As per December 2019 Cordova requires android-28 (Android 9.0 - Pie) so be sure to include it. Click on "Apply" to install the SDKs.
 
   ![SDK selection](https://cdn.quasar.dev/img/Android-Studio-SDK-selection.png "SDK selection")