Fix description of source code installer

The mkdocs version of INSTALL_SOURCE.md has disappeared and I am patching this in
so that users find the correct installer.

Author: lstein

docs/installation/index.md

@@ -5,8 +5,7 @@ title: Overview
 We offer several ways to install InvokeAI, each one suited to your
 experience and preferences.
 
-1. [InvokeAI source code installer](INSTALL_SOURCE.md)
-
+1. InvokeAI source code installer
     This is a script that will install Python, the Anaconda ("conda")
     package manager, all of InvokeAI's its essential third party
     libraries and InvokeAI itself. It includes access to a "developer
@@ -18,6 +17,14 @@ experience and preferences.
     script. This method is recommended for individuals who wish to
     stay on the cutting edge of InvokeAI development and are not
     afraid of occasional breakage.
+    
+    To get started go to the bottom of the [Latest Release Page](https://github.com/invoke-ai/InvokeAI/releases/latest)
+    and download the .zip file for your platform. Unzip the file.
+    If you are on a Windows system, double-click on the `install.bat`
+    script. On a Mac or Linux system, navigate to the file `install.sh`
+    from within the terminal application, and run the script.
+    
+    Sit back and watch the script run.
 
     **Important Caveats**
     - This script is a bit cranky and occasionally hangs or times out,