Merge pull request premake#1745 from hannes-harnisch/master

Adding documentation for module options

Author: KyrietS

website/docs/compileas.md

@@ -12,17 +12,17 @@ compileas "value"
 * `C++` - Compile as a C++ source file.
 * `Objective-C` - Compile as an Objective-C source file.
 * `Objective-C++` - Compile as an Objective-C++ source file.
-* `Module` - Needs documentation
-* `ModulePartition` - Needs documentation
-* `HeaderUnit` - Needs documentation
+* `Module` - Compile as a C++20 module interface unit.
+* `ModulePartition` - Compile as a C++20 module interface partition.
+* `HeaderUnit` - Compile as a C++20 header unit.
 
 ### Applies To ###
 
 The `workspace`, `project` or `file` scope.
 
 ### Availability ###
 
-Premake 5.0.0 alpha 13 or later.
+Premake 5.0.0 alpha 13 or later. The options **Module**, **ModulePartition** and **HeaderUnit** are only available in Premake 5.0-beta1 or later and only implemented for Visual Studio 2019+.
 
 ### Examples ###