Minimal async documentation.

Author: fredericDelaporte

doc/reference/modules/quickstart.xml

@@ -420,6 +420,12 @@ finally
             cases.
         </para>
 
+        <para>
+            Since NHibernate 5.0, the session and its queries IO bound methods have async counterparts.
+            Each call to an async method must be awaited before further interacting with the session or
+            its queries.
+        </para>
+
     </sect1>
 
     <sect1 id="quickstart-summary">

doc/reference/modules/transactions.xml

@@ -93,6 +93,11 @@
                     Never access the same <literal>ISession</literal> in two concurrent threads.
                     An <literal>ISession</literal> is usually only a single unit-of-work!
                 </para>
+                <para>
+                    Since NHibernate 5.0, the session and its queries IO bound methods have async counterparts.
+                    Each call to an async method must be awaited before further interacting with the session or
+                    its queries.
+                </para>
             </listitem>
         </itemizedlist>
     </sect1>