Enhance Build-Release.yml with comments and documentation link

Add comments to explain the workflow purpose and link to documentation.

Author: swmal

.github/workflows/Build-Release.yml

@@ -1,3 +1,7 @@
+# This workflow will build, test, sign and pack the release branches for EPPlus.
+# It will also generate and publish an SBOM
+# For more information see: https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-net
+
 name: Build Release Branches
 
 on: