update: add = for os in domain.md in docs/resources (#1209)

Signed-off-by: Ali Mehraji <a.mehraji75@gmail.com>

Author: cod3mas0n

docs/resources/domain.md

@@ -26,7 +26,7 @@ resource "libvirt_domain" "example" {
   vcpu   = 2
   type   = "kvm"
 
-  os {
+  os = {
     type    = "hvm"
     type_arch    = "x86_64"
     type_machine = "q35"