[docs] major update

docs/user/buying/docs.user.buying.md

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+---
+{
+	"_label": "Buying",
+	"_toc": [
+		"docs.user.buying.supplier_type",
+		"docs.user.buying.supplier",
+		"docs.user.buying.material_request",
+		"docs.user.buying.supplier_quotation",
+		"docs.user.buying.purchase_order",
+		"docs.user.buying.purchase_taxes",
+		"docs.user.buying.price_lists",
+		"docs.user.buying.sub_contracting"
+	]
+}
+---
+
+
+
+![Buying](img/buying-home.png)
+
+
+
+
+If your business involves physical goods, buying is one of your core business activity. Your suppliers are as important as your customers and they must be provided with as much accurate information as possible.
+
+Buying in right amounts, in right quantities, can affect your cash flow and profitability.
+
+ERPNext contains a set of transactions that will make your buying process as efficient and seamless as possible.