[docs] made structure for user docs combining manual and existing help

docs/docs.user.mfg.planning.md

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+---
+{
+	"_label": "Production Planning Tool"
+}
+---
+Production Planning Tool helps you plan production and purchase of Items for a period (usually a week or a month).
+
+This list of Items can be generated from the open Sales Orders in the system and will generate:
+
+- Production Orders for each Item.
+- Purchase Requests for Items whose Projected Quantity is likely to fall below zero.
+
+To use the Production Planning Tool, go to:

+
+> Manufacturing > Production Planning Tool
+
+The Production Planning Tool is used in two stages:
+
+- Selection of Open Sales Orders for the period based on “Expected Delivery Date”.
+- Selection of Items from those Sales Orders.
+- Click on “Raise Production Orders” 
+
+The tool will update if you have already created Production Orders for this Item against this Sales Order (“Planned Quantity”).
+
+You can always edit the Item list and increase / reduce quantities to plan your production.
+
+> Note: How do you change a Production Plan? The output of the Production Planning Tool is the Production Order. Once your orders are created, you can change them by amending the Production Orders.
+