[doc] Improve documentation of entity + signals.

doc/additionalDoc/entity.h

@@ -9,7 +9,7 @@ Despite the fact that it looks very similar to a ROS node or a CORBA/OpenRTM ser
 The main idea is that this entity is providing mostly a data-driven functionnality working at very high rate (\f$ 200 Hz\f$ or \f$ 1 kHz \f$)
 and should have a minimal computational time foot-print.
 
-For this signals (or ports to use a more classical terminology) are providing a time dependency between data.
+For this \subpage subp_signals (or ports to use a more classical terminology) are providing a time dependency between data.
 To implement this, an output signal is linked with a method of the entity. The method calls input signals or use other means
 to get the needed data.
 It might be provided by the connection with remote computers through a middleware, or specific protocols,

doc/additionalDoc/signal.h

@@ -2,7 +2,9 @@
 \page subp_signals Signals
 \section sec_sigintro Signals
 
-Entities can output different types of signals. All signals are templated by a Time
+Entities can output different types of signals. To guarante real-time perforamces, signals are implemented
+using C++ and mecanism which have a low time foot-print.
+All signals are templated by a Time
 tick type parameter (which is used in the caching of signals) - usually \c int. Signals
 are also templated after the type of data they accept or provide. For example:
 (example)