[commands] Elaborate more on disallowed types in Greedy and Optional

docs/ext/commands/commands.rst

@@ -471,6 +471,10 @@ Consider the following example:
 In this example, since the argument could not be converted into an ``int``, the default of ``99`` is passed and the parser
 resumes handling, which in this case would be to pass it into the ``liquid`` parameter.
 
+.. note::
+
+    This converter only works in regular positional parameters, not variable parameters or keyword-only parameters.
+
 Greedy
 ^^^^^^^^
 
@@ -533,6 +537,9 @@ This command can be invoked any of the following ways:
     unintended parsing ambiguities in your code. One technique would be to clamp down the expected syntaxes
     allowed through custom converters or reordering the parameters to minimise clashes.
 
+    To help aid with some parsing ambiguities, :class:`str`, ``None`` and :data:`~ext.commands.Greedy` are
+    forbidden as parameters for the :data:`~ext.commands.Greedy` converter.
+
 .. _ext_commands_error_handler:
 
 Error Handling