Add asyncio.md to ex_doc extras configuration

Author: benoitc

rebar.config

@@ -43,6 +43,7 @@
         <<"docs/memory.md">>,
         <<"docs/scalability.md">>,
         <<"docs/threading.md">>,
+        <<"docs/asyncio.md">>,
         <<"docs/testing-free-threading.md">>
     ]},
     {groups_for_extras, [
@@ -57,6 +58,7 @@
         {<<"Advanced">>, [
             <<"docs/scalability.md">>,
             <<"docs/threading.md">>,
+            <<"docs/asyncio.md">>,
             <<"docs/testing-free-threading.md">>
         ]}
     ]}