fix: Add async modules to the readthedocs API reference (#513)

Author: jsonbailey

docs/api-main.rst

@@ -13,13 +13,26 @@ ldclient.client module
 .. automodule:: ldclient.client
     :members: LDClient
 
+ldclient.async_client module
+----------------------------
+
+.. automodule:: ldclient.async_client
+    :members: AsyncLDClient
+
 ldclient.config module
 ----------------------
 
 .. automodule:: ldclient.config
     :members:
     :special-members: __init__
 
+ldclient.async_config module
+----------------------------
+
+.. automodule:: ldclient.async_config
+    :members:
+    :special-members: __init__
+
 ldclient.datasystem module
 --------------------------
 
@@ -33,6 +46,12 @@ ldclient.hook module
 .. automodule:: ldclient.hook
     :members:
 
+ldclient.plugin module
+----------------------
+
+.. automodule:: ldclient.plugin
+    :members:
+
 ldclient.evaluation module
 --------------------------