Improve performance of DSC resource integration tests by optimizing source change checks and update README with flow diagram

Author: johlju

CHANGELOG.md

@@ -81,7 +81,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Bump actions/checkout task to v5.
 - `.build/Test-ShouldRunDscResourceIntegrationTests.ps1`
   - Improved performance by adding an early optimization to check for changes
-    under the source folder before expensive analysis.
+    under the configured SourcePath before expensive analysis.
   - Moved public command discovery to only run when source changes are detected.
 - `.build/README.md`
   - Added flow diagram showing decision process for DSC resource integration tests.