Order status codes (#460)

* Add status code information for Sales Orders

* Add status codes for purchase orders

docs/buy/po.md

@@ -12,11 +12,18 @@ To access the purchase order page, click on the <span class="badge inventree nav
 {% include "img.html" %}
 {% endwith %}
 
-### Purchase Order Reference
+### Purchase Order Status Codes
 
-Each Purchase Order is uniquely identified by its *Reference* field. Read more about [reference fields](../settings/reference.md).
+Each Purchase Order has a specific status code which indicates the current state of the order:
 
-### Create Purchase Order
+| Status | Description |
+| --- | --- |
+| Pending | The purchase order has been created, but has not been submitted to the supplier |
+| In Progress | The purchase order has been issued to the supplier, and is in progress |
+| Complete | The purchase order has been completed, and is now closed |
+| Cancelled | The purchase order was cancelled, and is now closed |
+
+## Create Purchase Order
 
 Once the purchase order page is loaded, click on <span class="badge inventree add"><span class='fas fa-plus-circle'></span> New Purchase Order</span> which opens the "Create Purchase Order" form.
 
@@ -27,6 +34,10 @@ A purchase order is linked to a specific supplier, select one in the list of exi
 
 Fill out the rest of the form with the purchase order information then click on <span class="badge inventree confirm">Submit</span> 
 
+### Purchase Order Reference
+
+Each Purchase Order is uniquely identified by its *Reference* field. Read more about [reference fields](../settings/reference.md).
+
 ### Add Line Items
 
 On the purchase order detail page, user can link parts to the purchase order selecting the <span class="badge inventree nav side"><span class='fas fa-list'></span> Order Items</span> tab then clicking on the <span class="badge inventree add"><span class='fas fa-plus-circle'></span> Add Line Item</span> button.