fix: correct grammar in PRD workflow description (#1087)

Author: alexeyv

src/modules/bmm/workflows/2-plan-workflows/prd/workflow.md

@@ -1,6 +1,6 @@
 ---
 name: create-prd
-description: Creates a comprehensive PRDs through collaborative step-by-step discovery between two product managers working as peers.
+description: Creates a comprehensive PRD through collaborative step-by-step discovery between two product managers working as peers.
 main_config: '{project-root}/.bmad/bmm/config.yaml'
 web_bundle: true
 ---