Improve Windows Install instructions

[ctrlaltdavid]

https://docs.vircadia.com/explore/get-started/install.html

• The "Download Vircadia" sections lists both the installer and the launcher. However, the "Windows Install" section only mentions using the installer.
• The "Windows Install" section should include what Start Menu items are installed - for both launcher and installer - so that people can find them subsequent to the install step.
• The "Upgrade Vircadia" section doesn't included how to upgrade using the launcher as opposed to the installer.