docs: Add comment to ReadMe

Author: deadlydog

ReadMe.md

@@ -14,6 +14,7 @@
 </p>
 
 <p align="center">
+  <!-- Must add 'Windows', 'MacOS', and 'Linux' to the module manifest tags for them to show up on the Platforms badge. -->
   <img src="https://img.shields.io/powershellgallery/p/ScriptModuleRepositoryTemplate.svg">
   <img src="https://img.shields.io/github/languages/top/deadlydog/PowerShell.ScriptModuleRepositoryTemplate.svg">
   <img src="https://img.shields.io/github/languages/code-size/deadlydog/PowerShell.ScriptModuleRepositoryTemplate.svg">