Add (semi-depreciation) warning about colors parser in playground page

Author: AliSoftware

SwiftGen.playground/Pages/Colors-Demo.xcplaygroundpage/Contents.swift

@@ -11,6 +11,8 @@
 //: * [Demo for `yaml` parser](YAML-Demo)
 
 //: #### Example of code generated by `colors` parser with "literals-swift4" template
+//:  - Note: The `colors` parsers is primarily aimed to parse Android `colors.xml` files and text files.
+//:          In most cases, you should prefer defining your colors in asset catalogs – as those support multiple variants for light/dark mode, P3 colorspace, and more – and use the `xcassets` parser instead to generate constants for those colors.
 
 #if os(OSX)
   import AppKit