(GH-1054) Document requested execution levels

Document requestedExecutionLevel and how each applies and changes the
behavior of Chocolatey. Note that folks will need to do this every time
they upgrade until GH-1206 is implemented.

src/chocolatey.console/choco.exe.manifest

@@ -5,16 +5,28 @@
     <security>
       <requestedPrivileges xmlns="urn:schemas-microsoft-com:asm.v3">
         <!-- UAC Manifest Options
-            If you want to change the Windows User Account Control level replace the 
-            requestedExecutionLevel node with one of the following.
-
-            <requestedExecutionLevel  level="asInvoker" uiAccess="false" />
-            <requestedExecutionLevel  level="requireAdministrator" uiAccess="false" />
-            <requestedExecutionLevel  level="highestAvailable" uiAccess="false" />
-
-            Specifying requestedExecutionLevel node will disable file and registry virtualization.
-            If you want to utilize File and Registry Virtualization for backward 
-            compatibility then delete the requestedExecutionLevel node.
+            Specifying requestedExecutionLevel node (below) will disable file and 
+             registry virtualization.
+           
+            Set level to "asInvoker" when you want choco to run under the context
+             of the user invoking. This is the same as Chocolatey behavior prior 
+             to 0.10.4.
+             
+            Set level to "requireAdministrator" to only allow administrators to 
+             run Chocolatey.
+            
+            Set level to "highestAvailable" to allow non-admins to run in 
+             non-administrative context, but require administrators to always run
+             with administrative privileges. This is the recommended and default
+             behavior of Chocolatey v0.10.4+.
+            
+            NOTE: Currently you will need to make this change every time 
+             Chocolatey is re-installed or upgraded (every new version). At least
+             for now - https://github.com/chocolatey/choco/issues/1206
+            
+            The following is an unsupported use case: If you want to utilize File 
+             and Registry Virtualization for backward compatibility then delete 
+             the requestedExecutionLevel node.
         -->
         <requestedExecutionLevel level="highestAvailable" uiAccess="false" />
       </requestedPrivileges>