[doc] Add note about client options values returned by callables.

Predis will not attempt to use its standard configuration path for
options when using callables as initializers, this makes sense and
it is an intended behavior to give users more flexibility over the
configuration of the client but it can be confusing and unexpected
in certain cases such as with the combination of server profile and
key prefix.

doc/client.rst

@@ -146,6 +146,11 @@ them to `Client`::
        },
    ));
 
+.. note::
+   When using callables, the configuration of the returned value must be fully
+   handled by the user's code since Predis will not attempt to use its standard
+   configuration path for that option.
+
 Users can also specify their own custom options to pass additional information.
 Just like standard options, they are accessible from callable initializers::
 
@@ -196,6 +201,11 @@ profile         Changes the Redis version `Client` is expected to       2.6
                 a `Predis\\Profile\\ServerProfileInterface`
                 or its instance passed either directly or returned by
                 a callable initializer.
+
+                .. note::
+                   In the latter case, Predis will not automatically
+                   apply the specified key prefix to the profile so
+                   it must be manually set by the user's code.
 --------------  ------------------------------------------------------  ------------------------------------------------
 connections     Overrides :doc:`connection backends` by scheme using    - tcp: `Predis\\Connection\\StreamConnection`
                 a named array, with keys being the connection schemes   - unix: `Predis\\Connection\\StreamConnection`