Improve glob handling for source paths and update docs

- Simplify glob handling in TailwindCSSBuildPlugin to support **
patterns - Update README and Tailwind.css example to clarify glob usage
- Add Template.swift example using Tailwind classes - Extend tests to
verify class extraction from globbed Swift files

Sources/SwiftTailwindExample/Folder/Template.swift

@@ -0,0 +1,4 @@
+let template =
+"""
+<div class="bg-red-100">Test</div>
+"""

Sources/SwiftTailwindExample/Tailwind.css

@@ -5,3 +5,4 @@
 @import "tailwindcss" source(none);
 @source "./Example.swift";
 @source "./Folder";
+@source "./Folder/**/*.swift";