OpenStack builder: fix floating IP docs

Update website documentation about "floating_ip_network" parameter.
Add new inline comment about alghoritm that is used for checking
floatingIP-related configuration parameters.

builder/openstack/step_allocate_ip.go

@@ -43,7 +43,12 @@ func (s *StepAllocateIp) Run(_ context.Context, state multistep.StateBag) multis
 	// statebag below, because it is requested by Cleanup()
 	state.Put("access_ip", &instanceIP)
 
-	// WRITE NEW COMMENT>
+	// Try to Use the OpenStack floating IP by checking provided parameters in
+	// the following order:
+	//  - try to use "FloatingIP" ID directly if it's provided
+	//  - try to find free floating IP in the project if "ReuseIPs" is set
+	//  - create a new floating IP if "FloatingIPNetwork" is provided (it can be
+	//    ID or name of the network).
 	if s.FloatingIP != "" {
 		// Try to use FloatingIP if it was provided by the user.
 		freeFloatingIP, err := CheckFloatingIP(networkClient, s.FloatingIP)

website/source/docs/builders/openstack.html.md

@@ -112,8 +112,8 @@ builder.
 
 -   `floating_ip` (string) - A specific floating IP to assign to this instance.
 
--   `floating_ip_network` (string) - The ID of an external network that can be
-    used for creation of a new floating IP.
+-   `floating_ip_network` (string) - The ID or name of an external network that
+    can be used for creation of a new floating IP.
 
 -   `floating_ip_pool` (string) - *Deprecated* use `floating_ip_network`
     instead.