doc/: comment out the concept index

doc/chapters/introduction.texi

@@ -80,12 +80,14 @@ The remainder of this section describes the main concepts used in StarPU.
 @node Codelet and Tasks
 @subsection Codelet and Tasks
 
+@cindex codelet
 One of the StarPU primary data structures is the @b{codelet}. A codelet describes a
 computational kernel that can possibly be implemented on multiple architectures
 such as a CPU, a CUDA device or a Cell's SPU.
 
 @c TODO insert illustration f: f_spu, f_cpu, ...
 
+@cindex task
 Another important data structure is the @b{task}. Executing a StarPU task
 consists in applying a codelet on a data set, on one of the architectures on
 which the codelet is implemented. A task thus describes the codelet that it
@@ -97,6 +99,7 @@ called once StarPU has properly executed the task. It also contains optional
 fields that the application may use to give hints to the scheduler (such as
 priority levels).
 
+@cindex tag
 By default, task dependencies are inferred from data dependency (sequential
 coherence) by StarPU. The application can however disable sequential coherency
 for some data, and dependencies be expressed by hand.

doc/starpu.texi

@@ -230,6 +230,8 @@ was last updated on @value{UPDATED}.
 @c Indices
 @c ---------------------------------------------------------------------
 
+@c comment it out for now, it is too small to be kept for now. See how
+@c it can be merged with the glossary section in the introduction
 @node Concept Index
 @unnumbered Concept Index
 @printindex cp