Propagate text updates to developer guide (#2313)

This changelist propagates recent text updates from the front page to the Developer Guide for consistency.

Author: jstone-lucasfilm

documents/DeveloperGuide/MainPage.md

@@ -7,7 +7,8 @@ MaterialX is an open standard for representing rich material and look-developmen
 - Download the latest version of the [CMake](https://cmake.org/) build system.
 - Point CMake to the root of the MaterialX library and generate C++ projects for your platform and compiler.
 - Select the `MATERIALX_BUILD_PYTHON` option to build Python bindings.
-- Select the `MATERIALX_BUILD_VIEWER` option to build the MaterialX viewer.
+- Select the `MATERIALX_BUILD_VIEWER` option to build the [MaterialX Viewer](https://github.com/AcademySoftwareFoundation/MaterialX/blob/main/documents/DeveloperGuide/Viewer.md).
+- Select the `MATERIALX_BUILD_GRAPH_EDITOR` option to build the [MaterialX Graph Editor](https://github.com/AcademySoftwareFoundation/MaterialX/blob/main/documents/DeveloperGuide/GraphEditor.md). 
 
 ## Supported Platforms