Reorganized the Workflow docs

Author: javiereguiluz

_build/redirection_map

@@ -362,3 +362,5 @@
 /console/logging /console
 /frontend/encore/legacy-apps /frontend/encore/legacy-applications
 /contributing/code/patches /contributing/code/pull_requests
+/workflow/state-machines /workflow/introduction
+/workflow/usage /workflow