Add: Finding Primary storage for migration (#325)

Adding a section describing how cloudstack finds a suitable primary storage for migration.

Author: rajujith

source/adminguide/storage.rst

@@ -730,13 +730,18 @@ be restarted.
 
 Finding Primary Storage for Migration
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-When you click on migrate volume, CloudStack lists the available primary storage.  CloudStack uses its storage pool allocators to identify the primary storages that are available and returns a list that is suitable for the selected volume's migration. 
-The list also could include primary storages that are mentioned as 'Not suitable'. The criteria for which the primary storages are not suitable are: 
-	- Storage tag mismatch with the volume's Disk offering's storage tag
-	- Doesn't have enough capacity. 
-	- Reached its disable threshold
-	- Disabled. 
-	- Mismatch in the type of storage such as Shared /Local. 
+
+When you click on migrate volume, CloudStack lists the available primary
+storage.  CloudStack uses its storage pool allocators to identify the primary
+storages that are available and returns a list that is suitable for the selected
+volume's migration. 
+The list also could include primary storages that are mentioned as
+'Not suitable'. The criteria for which the primary storages are not suitable are: 
+-  Storage tag mismatch with the volume.
+-  Doesn't have enough capacity. 
+-  Reached its disable threshold.
+-  Disabled.
+-  Mismatch in the type of storage such as shared /Local. 
 
 Resizing Volumes
 ~~~~~~~~~~~~~~~~